Goal:
  
  A : Type
  B : Type
  C : Type
  P : A → B → Type
  Q : B → C → Type
  R : A → C → Type
  ============================
   (let H := CoreTactics.block in
    let H0 := CoreTactics.block in
    (∀ (x : A) (y : B) (z : C), P x y → Q y z → R x z) → All2 R [] [])


DEBUG:Going to execute:
match goal with
           | hyp:context [ CoreTactics.block ]
             |- _ =>
                 cbn beta in hyp; eqns_specialize_eqs_block hyp;
                  cbn[eq_rect_r eq_rect] in hyp
           end