Prove syntactic char -> semantic char

Project2.fst

@@ -223,7 +223,7 @@ val nsteps_stop: (n: nat) -> (te:tenv) -> (cs: callstack{wellformed cs}) ->
 Lemma (requires (isFinal cs))
       (ensures (nsteps n te cs == cs))
 let rec nsteps_stop n te cs =
- admit ()
+  if n = 0 then () else nsteps_stop (n-1) te (step_simp te cs)
 
 (* Prove that if a call stack does not change within one step then it must be final. Formulate first the Lemma and then prove it *)
 (* val progress: *)