Goal:
  
  A : Type
  f : A -> bool
  g : A -> bool
  Hfg : f =1 g
  f' : A -> bool
  g' : A -> bool
  Hfg' : f' =1 g'
  i : A
  ============================
   (g i ==> g' i = g i ==> g' i)


DEBUG:Going to execute:
let do_atom := solve
           [ trivial
           with eq_true
           | reflexivity
           | symmetry; trivial
           | contradiction
           | congruence ]
           in
           let rec do_ccl :=
            try do_atom; repeat (do_intro; try do_atom); try arith_congr;
             (solve [ split; do_ccl ])
           in
           (solve [ do_atom | use_hyps; do_ccl ]) ||
             fail "Cannot solve this goal"