CCEqualSourceEquality function. Must be transitive, symmetric, and reflexive.
map f eq is the equality function that, given objects x and y, projects x and y using f (e.g. using a record field) and then compares those projections with eq. Example: map fst int compares values of type (int * 'a) by their first component.
Always returns false. No values are, so this is not even reflexive (i.e. x=x is false). Be careful!