Suppose that we have three Z->Z functions such as f, g and h. How should f and h be so that f o g o h can be onto (surjective) given that g is a one to one (injective) function?

adarascarlet80

adarascarlet80

Answered question

2022-10-05

Suppose that we have three Z Z functions such as f, g and h. How should f and h be so that f∘g∘h can be onto (surjective) given that g is a one to one (injective) function?

Answer & Explanation

Jasmin Hoffman

Jasmin Hoffman

Beginner2022-10-06Added 6 answers

There’s not much that you can say. Suppose that h [ Z ] = A and f g h; f g h is a surjection if and only if f [ B ] = Z . This in turn requires that B be infinite, which means that A must be infinite. Thus, h must have an infinite range A, and f must map g [ A ] onto Z , but that’s about all that you can say in general. In particular, it’s not enough to require that h and f be surjections: a counterexample is obtained by taking h and f to be the identity functions and g : Z Z : n 2 n, in which case f g h maps Z to the even integers.

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