Discrete mathematics structural induction 2/23. Slide 7 contains another definitional use of induction. More induction spring 2020 created by: Structural induction is a method for proving that all the elements of a recursively defined data type have some property. Let (a, (fi)i∈i) ( a, ( f i) i ∈ i) be a set and a family of functions fi:

Let p(x) be the statement len(x) ≥ 0 . A structural induction proof has two parts corresponding to the recursive definition: Slide 7 contains another definitional use of induction. If various instances of a schema are true and there are no counterexamples, we are tempted to conclude a universally quantified version of the schema.

For structural induction, we are wanting to show that for a discrete parameter n holds such that: Then, len(concat(nil, r)) = len(r) = 0 + len(r) = len(nil) + len(r) , showing p(nil). = ε ∣ xa and len:

Recall σ ∗ is defined by x ∈ σ ∗:: For structural induction, we are wanting to show that for a discrete parameter n holds such that: Suppose ( ) for an arbitrary string inductive step: This technique is known as structural induction, and is induction defined over the domain It is a generalization of mathematical induction over natural numbers and can be further generalized to arbitrary noetherian induction.

Web istuctural inductionis a technique that allows us to apply induction on recursive de nitions even if there is no integer. Let p(x) be the statement len(x) ≥ 0 . Istructural induction is also no more powerful than regular induction, but can make proofs much easier.

The Set N Of Natural Numbers Is The Set Of Elements Defined By The Following Rules:

We will learn many, and all are on the. P(snfeng) !p(s) is true, so p(s) is true. Let r∈ list be arbitrary. Thus the elements of n are {0, s0, ss0, sss0,.}.

We Will Prove The Theorem By Structural Induction Over D.

If n ∈ n then sn ∈ n. Let be an arbitrary string, len( ⋅ )=len(x) =len(x)+0=len(x)+len( ) inductive hypothesis: Since s s is well founded q q contains a minimal element m m. Web this more general form of induction is often called structural induction.

Slide 7 Contains Another Definitional Use Of Induction.

For all x ∈ σ ∗, len(x) ≥ 0 proof: Let = for an arbitrary ∈ σ. Recall that structural induction is a method for proving statements about recursively de ned sets. The factorial function fact is defined inductively on the natural.

Let D Be A Derivation Of Judgment Hc;˙I + ˙0.

, where is the empty string. Empty tree, tree with one node node with left and right subtrees. Assume that p(l) is true for some arbitrary l∈ list, i.e., len(concat(l, r)) = len(l) + len(r) for all r ∈ list. For example, slide 6 gives an inductive definition of the factorial function over the natural numbers.

Let ( ) be “len(x⋅y)=len(x) + len(y) for all ∈ σ∗. The set n of natural numbers is the set of elements defined by the following rules: Let r∈ list be arbitrary. Incomplete induction is induction where the set of instances is not exhaustive. Discrete mathematics structural induction 2/23.