Which of the following is an equivalence relation on the set of all functions from Z to Z ?
1
{ (f, g) | f (x) − g (x) = 1 x ϵ Z }
2
{ (f, g) | f (0) = g (0) or f (1) = g (1) }
3
{ (f, g) | f (0) = g (1) and f (1) = g (0) }
4
{ (f, g) | f (x) − g (x) = k for some k ϵ Z }