Goal:
    x : t  y : t  z : t  H : lt x y  H0 : lt x z
  ============================
   (lt x z)


DEBUG:Going to execute:
let rec do_ccl :=
            try do_atom; repeat (do_intro; try do_atom); (solve
             [ Ltac.split; do_ccl ])
           in
           (solve [ do_atom | use_hyps; do_ccl ]) ||
             fail "Cannot solve this goal"