open tactic



example (a b c : nat) (H : c = b) : a + c = a + b :=
by do
  N ← to_expr `(nat),
  define `v N,
  trace_state,
  trace  "------------",
  to_expr `(a + b) >>= exact,
  trace_state,
  trace "------------",
  get_local `H >>= subst,
  trace_state,
  to_expr `(eq.refl v) >>= exact