Question

define a function f:A->B
such that A = {..., -8, -4, 0, 4, 8,...}
and B = Natural Numbers

Answer 1

well, if we were to a mapping of B into A ..

A = 4n would suffice, im thinking B = |A/4| would suffice, but then does your text define 0 is a natural ?

Answer 2

B = |A/4|+1 might be good