a, b:, c:. ((a -- b) -- c) = (a -- (b+c))   

latex

Up	int 2, int 2
Definitions	t  T, a -- b, x:A. B(x), T, , True, P  Q, P & Q, P  Q, P  Q, ff, tt, if b then t else f fi , imax(a;b), , Unit, , False, A, A  B,
Lemmas	nat wf, true wf, squash wf, imax wf, imax add r, add com, imax assoc, assert of lt int, bnot of le int, eqff to assert, assert of le int, eqtt to assert, iff transitivity, bnot wf, lt int wf, le wf, assert wf, bool wf, le int wf