Goal:
    hd' : A.t  tl' : list A.t  hd : A.t  tl : list A.t  H : A.lt hd hd'
  ============================
   (let H := CoreTactics.block in
    let H0 := CoreTactics.block in lt [] (hd' :: tl'))


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