Definition eq_sind_r :
forall (A:Type) (x:A) (P:A -> SProp), P x -> forall y:A, y = x -> P y.
Register f_equal2 as core.eq.congr2.

Theorem f_equal_compose A B C (a b:A) (f:A->B) (g:B->C) (e:a=b) :
f_equal g (f_equal f e) = f_equal (fun a => g (f a)) e.