Question 4-1

Using the Church numerals, we can define the inc function in the lambda calculus to take a Church numeral representing some number n and return the Church numeral representing n+1.

inc = λasz.a s (s z)
Give a lambda calculus definition of the addition function +, which takes two Church numerals representing two numbers m and n and returns a Church numeral representing their sum, m+n.

Solution

λmn.n inc m

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