Goal:
  
  A : Type
  sizeA : A → nat
  B : Type
  sizeB : B → nat
  l : list A
  f : nat → A → B
  H : ∀ (i : nat) (x : A), sizeB (f i x) ≤ sizeA x
  ============================
   (∀ (i : nat) (x : A), sizeB (f i x) ≤ sizeA x)


DEBUG:Going to execute:
PTRDEBUGTAClet 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"