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_equal3 :
forall (A1 A2 A3 B:Type) (f:A1 -> A2 -> A3 -> B) (x1 y1:A1)
(x2 y2:A2) (x3 y3:A3),
x1 = y1 -> x2 = y2 -> x3 = y3 -> f x1 x2 x3 = f y1 y2 y3.