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The Principle of Induction Examples Strong Induction Associativity Induction Bernd Schr oder logo1 Bernd Schr oder Louisiana Tech University, College of Engineering and Science Induction The Principle of Induction Examples Strong
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Let P ( n ) be a statement about the natural number n. If P ( 1 ) is true and if, for all n ∈ N , truth of P ( n ) implies truth of P ( n + 1 ) , then P ( n ) holds for all natural numbers. � � Proof. Consider the set S : = n ∈ N : P ( n ) is true . Then 1 ∈ S . Moreover, if n ∈ S , then the statement P ( n ) is true. By assumption, this implies that P ( n + 1 ) is true. That is, n + 1 ∈ S . By the Principle of Induction, S = N . Thus for all n ∈ N the statement P ( n ) is true. The proof of P ( 1 ) is also called the base step of the induction. The proof that P ( n ) implies P ( n + 1 ) is also called the induction step . logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. For all n ∈ N we have that 1 + 2 + 3 + ··· + n = n ( n + 1 ) . 2 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. For all n ∈ N we have that 1 + 2 + 3 + ··· + n = n ( n + 1 ) . 2 Base step, n = 1 . logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. For all n ∈ N we have that 1 + 2 + 3 + ··· + n = n ( n + 1 ) . 2 Base step, n = 1 . 1 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. For all n ∈ N we have that 1 + 2 + 3 + ··· + n = n ( n + 1 ) . 2 Base step, n = 1 . 1 = 1 ( 1 + 1 ) . 2 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. For all n ∈ N we have that 1 + 2 + 3 + ··· + n = n ( n + 1 ) . 2 Base step, n = 1 . 1 = 1 ( 1 + 1 ) . 2 Induction step n → n + 1 . logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. For all n ∈ N we have that 1 + 2 + 3 + ··· + n = n ( n + 1 ) . 2 Base step, n = 1 . 1 = 1 ( 1 + 1 ) . 2 Induction step n → n + 1 . 1 + 2 + 3 + ··· + n +( n + 1 ) logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. For all n ∈ N we have that 1 + 2 + 3 + ··· + n = n ( n + 1 ) . 2 Base step, n = 1 . 1 = 1 ( 1 + 1 ) . 2 Induction step n → n + 1 . n ( n + 1 ) 1 + 2 + 3 + ··· + n +( n + 1 ) = +( n + 1 ) 2 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. For all n ∈ N we have that 1 + 2 + 3 + ··· + n = n ( n + 1 ) . 2 Base step, n = 1 . 1 = 1 ( 1 + 1 ) . 2 Induction step n → n + 1 . n ( n + 1 ) 1 + 2 + 3 + ··· + n +( n + 1 ) = +( n + 1 ) 2 n ( n + 1 )+ 2 ( n + 1 ) = 2 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. For all n ∈ N we have that 1 + 2 + 3 + ··· + n = n ( n + 1 ) . 2 Base step, n = 1 . 1 = 1 ( 1 + 1 ) . 2 Induction step n → n + 1 . n ( n + 1 ) 1 + 2 + 3 + ··· + n +( n + 1 ) = +( n + 1 ) 2 n ( n + 1 )+ 2 ( n + 1 ) = 2 � � ( n + 1 ) ( n + 1 )+ 1 = 2 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. For all n ∈ N we have that 1 + 2 + 3 + ··· + n = n ( n + 1 ) . 2 Base step, n = 1 . 1 = 1 ( 1 + 1 ) . 2 Induction step n → n + 1 . n ( n + 1 ) 1 + 2 + 3 + ··· + n +( n + 1 ) = +( n + 1 ) 2 n ( n + 1 )+ 2 ( n + 1 ) = 2 � � ( n + 1 ) ( n + 1 )+ 1 = 2 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Base step logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Base step, n = 3 . logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Base step, n = 3 . (See book. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Base step, n = 3 . (See book. We also did quadrilaterals in the presentation on proofs.) logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Finding the right corner. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Finding the right corner. ✑✑✑✑✑✑ ☞ ☞ ☞ ☞ � ... � � � logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Finding the right corner. A k ✑✑✑✑✑✑ s ☞ ☞ ☞ ☞ � ... � � � logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Finding the right corner. A k ✑✑✑✑✑✑ s A k − 1 s ☞ ☞ ☞ ☞ � ... � � � logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Finding the right corner. A k ✑✑✑✑✑✑ s A k − 1 s ☞ ☞ ☞ ☞ s � A k + 1 ... � � � logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Finding the right corner. A k ✑✑✑✑✑✑ s A k − 1 s ☞ ☞ ☞ ☞ s � A k + 1 ... � � � logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Finding the right corner. A k ✑✑✑✑✑✑ s A k − 1 A j s ☞ ✑✑✑ s ☞ A j − 1 ☞ s ☞ s s � A j + 1 A k + 1 ... � � � logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Cutting a “convex corner”. A k ✑✑✑✑✑✑ s A k − 1 A j s ☞ ✑✑✑ s ☞ A j − 1 ☞ s ☞ s s � A j + 1 A k + 1 ... � � � logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Cutting a “convex corner”. A k ✑✑✑✑✑✑ s A k − 1 s ☞ ☞ ☞ ☞ s � A k + 1 ... � � � logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Cutting a “convex corner”. A k ✑✑✑✑✑✑ s A k − 1 s ☞ α k − 1 ☞ ☞ ☞ s � A k + 1 ... � � � logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Cutting a “convex corner”. A k ✑✑✑✑✑✑ s α k A k − 1 s ☞ α k − 1 ☞ ☞ ☞ s � A k + 1 ... � � � logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Cutting a “convex corner”. A k ✑✑✑✑✑✑ s α k A k − 1 s ☞ α k − 1 ☞ ☞ ☞ α k + 1 s � A k + 1 ... � � � logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Cutting a “concave corner”. A k ✑✑✑✑✑✑ s s A k − 1 s A k + 1 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Cutting a “concave corner”. A k ✆✆ ✑✑✑✑✑✑ s ✆ ✆ ✆ s A k − 1 s A k + 1 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Cutting a “concave corner”. ✘ ✘✘✘✘✘✘✘✘✘ A k ✆✆ ✑✑✑✑✑✑ s ✆ ✆ ✆ s A k − 1 s A k + 1 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Cutting a “concave corner”. ✘ ✘✘✘✘✘✘✘✘✘ A k ✆✆ ✑✑✑✑✑✑ s ✆ ✔ ✆ ✔ ✆ ✔ s ✔ A k − 1 ✔ ✔ ✔ ✔ s A k + 1 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Cutting a “concave corner”. ✘ ✘✘✘✘✘✘✘✘✘ ... A k ✆✆ ✑✑✑✑✑✑ s ✆ ✔ ✆ ✔ ✆ ✔ s ✔ A k − 1 ✔ ✔ ✔ ✔ s A k + 1 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Cutting a “concave corner”. ✘ ✘✘✘✘✘✘✘✘✘ ... A k ✆✆ ✑✑✑✑✑✑ s ✆ ✔ ✆ ✔ ✆ ✔ s ✔ A k − 1 ✔ ✔ ✔ ✔ s A k + 1 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Cutting a “concave corner”. ✘ ✘✘✘✘✘✘✘✘✘ ... A k ✆✆ ✑✑✑✑✑✑ s ✆ ✔ ✆ ✔ ✆ ✔ s ✔ A k − 1 ✔ ✔ ✔ ✔ s A k + 1 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Cutting a “concave corner”. ✘ ✘✘✘✘✘✘✘✘✘ ... A k ✆✆ ✑✑✑✑✑✑ s ✆ ✔ ✆ ✔ ✆ ✔ s ✔ A k − 1 ✔ ✔ ✔ ✔ s A k + 1 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Cutting a “concave corner”. ✘ ✘✘✘✘✘✘✘✘✘ ... A k ✆✆ ✑✑✑✑✑✑ s ✆ ✔ ✆ ✔ ✆ ✔ s α k − 1 ✔ A k − 1 ✔ ✔ ✔ ✔ s A k + 1 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Cutting a “concave corner”. ✘ ✘✘✘✘✘✘✘✘✘ ... A k ✆✆ ✑✑✑✑✑✑ s ✆ α k ✔ ✆ ✔ ✆ ✔ s α k − 1 ✔ A k − 1 ✔ ✔ ✔ ✔ s A k + 1 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Example. The sum of the interior angles of a plane n-gon with n ≥ 3 vertices is ( n − 2 ) π . Induction step. Cutting a “concave corner”. ✘ ✘✘✘✘✘✘✘✘✘ ... A k ✆✆ ✑✑✑✑✑✑ s ✆ α k ✔ ✆ ✔ ✆ ✔ s α k − 1 ✔ A k − 1 ✔ ✔ α k + 1 ✔ ✔ s A k + 1 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . Suppose for a contradiction that A does not have a smallest element. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . Suppose for a contradiction that A does not have a smallest element. Let P ( n ) = “ { 1 ,..., n }∩ A = / 0”. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . Suppose for a contradiction that A does not have a smallest element. Let P ( n ) = “ { 1 ,..., n }∩ A = / 0”. We will prove P ( n ) for all n ∈ N . logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . Suppose for a contradiction that A does not have a smallest element. Let P ( n ) = “ { 1 ,..., n }∩ A = / 0”. We will prove P ( n ) for all n ∈ N . Base step, n = 1 . logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . Suppose for a contradiction that A does not have a smallest element. Let P ( n ) = “ { 1 ,..., n }∩ A = / 0”. We will prove P ( n ) for all n ∈ N . Base step, n = 1 . 1 is the smallest element of N . logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . Suppose for a contradiction that A does not have a smallest element. Let P ( n ) = “ { 1 ,..., n }∩ A = / 0”. We will prove P ( n ) for all n ∈ N . Base step, n = 1 . 1 is the smallest element of N . So 1 �∈ A . logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . Suppose for a contradiction that A does not have a smallest element. Let P ( n ) = “ { 1 ,..., n }∩ A = / 0”. We will prove P ( n ) for all n ∈ N . Base step, n = 1 . 1 is the smallest element of N . So 1 �∈ A . Hence P ( 1 ) is true. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . Suppose for a contradiction that A does not have a smallest element. Let P ( n ) = “ { 1 ,..., n }∩ A = / 0”. We will prove P ( n ) for all n ∈ N . Base step, n = 1 . 1 is the smallest element of N . So 1 �∈ A . Hence P ( 1 ) is true. Induction step, n → n + 1 . logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . Suppose for a contradiction that A does not have a smallest element. Let P ( n ) = “ { 1 ,..., n }∩ A = / 0”. We will prove P ( n ) for all n ∈ N . Base step, n = 1 . 1 is the smallest element of N . So 1 �∈ A . Hence P ( 1 ) is true. Induction step, n → n + 1 . Assume { 1 ,..., n }∩ A = / 0 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . Suppose for a contradiction that A does not have a smallest element. Let P ( n ) = “ { 1 ,..., n }∩ A = / 0”. We will prove P ( n ) for all n ∈ N . Base step, n = 1 . 1 is the smallest element of N . So 1 �∈ A . Hence P ( 1 ) is true. Induction step, n → n + 1 . Assume { 1 ,..., n }∩ A = / 0 and consider the element n + 1. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . Suppose for a contradiction that A does not have a smallest element. Let P ( n ) = “ { 1 ,..., n }∩ A = / 0”. We will prove P ( n ) for all n ∈ N . Base step, n = 1 . 1 is the smallest element of N . So 1 �∈ A . Hence P ( 1 ) is true. Induction step, n → n + 1 . Assume { 1 ,..., n }∩ A = / 0 and consider the element n + 1. n + 1 is the smallest element of N \{ 1 ,..., n } . logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . Suppose for a contradiction that A does not have a smallest element. Let P ( n ) = “ { 1 ,..., n }∩ A = / 0”. We will prove P ( n ) for all n ∈ N . Base step, n = 1 . 1 is the smallest element of N . So 1 �∈ A . Hence P ( 1 ) is true. Induction step, n → n + 1 . Assume { 1 ,..., n }∩ A = / 0 and consider the element n + 1. n + 1 is the smallest element of N \{ 1 ,..., n } . Thus n + 1 �∈ A . logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . Suppose for a contradiction that A does not have a smallest element. Let P ( n ) = “ { 1 ,..., n }∩ A = / 0”. We will prove P ( n ) for all n ∈ N . Base step, n = 1 . 1 is the smallest element of N . So 1 �∈ A . Hence P ( 1 ) is true. Induction step, n → n + 1 . Assume { 1 ,..., n }∩ A = / 0 and consider the element n + 1. n + 1 is the smallest element of N \{ 1 ,..., n } . Thus n + 1 �∈ A . Hence P ( n + 1 ) is true. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . Suppose for a contradiction that A does not have a smallest element. Let P ( n ) = “ { 1 ,..., n }∩ A = / 0”. We will prove P ( n ) for all n ∈ N . Base step, n = 1 . 1 is the smallest element of N . So 1 �∈ A . Hence P ( 1 ) is true. Induction step, n → n + 1 . Assume { 1 ,..., n }∩ A = / 0 and consider the element n + 1. n + 1 is the smallest element of N \{ 1 ,..., n } . Thus n + 1 �∈ A . Hence P ( n + 1 ) is true. So P ( n ) holds for all n ∈ N logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . Suppose for a contradiction that A does not have a smallest element. Let P ( n ) = “ { 1 ,..., n }∩ A = / 0”. We will prove P ( n ) for all n ∈ N . Base step, n = 1 . 1 is the smallest element of N . So 1 �∈ A . Hence P ( 1 ) is true. Induction step, n → n + 1 . Assume { 1 ,..., n }∩ A = / 0 and consider the element n + 1. n + 1 is the smallest element of N \{ 1 ,..., n } . Thus n + 1 �∈ A . Hence P ( n + 1 ) is true. So P ( n ) holds for all n ∈ N and A is empty logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . Suppose for a contradiction that A does not have a smallest element. Let P ( n ) = “ { 1 ,..., n }∩ A = / 0”. We will prove P ( n ) for all n ∈ N . Base step, n = 1 . 1 is the smallest element of N . So 1 �∈ A . Hence P ( 1 ) is true. Induction step, n → n + 1 . Assume { 1 ,..., n }∩ A = / 0 and consider the element n + 1. n + 1 is the smallest element of N \{ 1 ,..., n } . Thus n + 1 �∈ A . Hence P ( n + 1 ) is true. So P ( n ) holds for all n ∈ N and A is empty, contradiction. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . Suppose for a contradiction that A does not have a smallest element. Let P ( n ) = “ { 1 ,..., n }∩ A = / 0”. We will prove P ( n ) for all n ∈ N . Base step, n = 1 . 1 is the smallest element of N . So 1 �∈ A . Hence P ( 1 ) is true. Induction step, n → n + 1 . Assume { 1 ,..., n }∩ A = / 0 and consider the element n + 1. n + 1 is the smallest element of N \{ 1 ,..., n } . Thus n + 1 �∈ A . Hence P ( n + 1 ) is true. So P ( n ) holds for all n ∈ N and A is empty, contradiction. Therefore A must have a smallest element. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Theorem. Principle of Induction. Every nonempty subset A of N has a smallest element. Proof. Let / 0 � = A ⊆ N . Suppose for a contradiction that A does not have a smallest element. Let P ( n ) = “ { 1 ,..., n }∩ A = / 0”. We will prove P ( n ) for all n ∈ N . Base step, n = 1 . 1 is the smallest element of N . So 1 �∈ A . Hence P ( 1 ) is true. Induction step, n → n + 1 . Assume { 1 ,..., n }∩ A = / 0 and consider the element n + 1. n + 1 is the smallest element of N \{ 1 ,..., n } . Thus n + 1 �∈ A . Hence P ( n + 1 ) is true. So P ( n ) holds for all n ∈ N and A is empty, contradiction. Therefore A must have a smallest element. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Definition. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Definition. A set F is called finite iff F is empty or there is an n ∈ N and a bijective function f : { 1 ,..., n } → F. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Definition. A set F is called finite iff F is empty or there is an n ∈ N and a bijective function f : { 1 ,..., n } → F. Sets that are not finite are called infinite . logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Definition. A set F is called finite iff F is empty or there is an n ∈ N and a bijective function f : { 1 ,..., n } → F. Sets that are not finite are called infinite . For finite sets F � = / 0 we set | F | : = n with n as above logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Definition. A set F is called finite iff F is empty or there is an n ∈ N and a bijective function f : { 1 ,..., n } → F. Sets that are not finite are called infinite . For finite sets F � = / 0 we set | F | : = n with n as above and we set | / 0 | : = 0 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Definition. A set F is called finite iff F is empty or there is an n ∈ N and a bijective function f : { 1 ,..., n } → F. Sets that are not finite are called infinite . For finite sets F � = / 0 we set | F | : = n with n as above and we set | / 0 | : = 0 , where 0 is an element that is not in N . logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Definition. A set F is called finite iff F is empty or there is an n ∈ N and a bijective function f : { 1 ,..., n } → F. Sets that are not finite are called infinite . For finite sets F � = / 0 we set | F | : = n with n as above and we set | / 0 | : = 0 , where 0 is an element that is not in N . For infinite sets I we set | I | : = ∞ , where ∞ is an element that is not in N ∪{ 0 } . logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Definition. A set F is called finite iff F is empty or there is an n ∈ N and a bijective function f : { 1 ,..., n } → F. Sets that are not finite are called infinite . For finite sets F � = / 0 we set | F | : = n with n as above and we set | / 0 | : = 0 , where 0 is an element that is not in N . For infinite sets I we set | I | : = ∞ , where ∞ is an element that is not in N ∪{ 0 } . Theorem. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Definition. A set F is called finite iff F is empty or there is an n ∈ N and a bijective function f : { 1 ,..., n } → F. Sets that are not finite are called infinite . For finite sets F � = / 0 we set | F | : = n with n as above and we set | / 0 | : = 0 , where 0 is an element that is not in N . For infinite sets I we set | I | : = ∞ , where ∞ is an element that is not in N ∪{ 0 } . Theorem. Let A and B be finite sets so that A ⊆ B and so that | A | = | B | . logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Definition. A set F is called finite iff F is empty or there is an n ∈ N and a bijective function f : { 1 ,..., n } → F. Sets that are not finite are called infinite . For finite sets F � = / 0 we set | F | : = n with n as above and we set | / 0 | : = 0 , where 0 is an element that is not in N . For infinite sets I we set | I | : = ∞ , where ∞ is an element that is not in N ∪{ 0 } . Theorem. Let A and B be finite sets so that A ⊆ B and so that | A | = | B | . Then A = B. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Proof. logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
The Principle of Induction Examples Strong Induction Associativity Proof. If | A | = 0, then | B | = | A | = 0 logo1 Bernd Schr¨ oder Louisiana Tech University, College of Engineering and Science Induction
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