Decomposing equality of constructors coq

Question

Often in Coq I find myself doing the following: I have the proof goal, for example:

some_constructor a c d = some_constructor b c d

And I r

Answer 1

In particular, standard Coq provides the f_equal tactic.

Inductive u : Type := U : nat -> nat -> nat -> u.

Lemma U1 x y z1 z2 : U x y z1 = U x y z2.
f_equal

Also, ssreflect provides a general-purpose congruence tactic congr.