Compute NNF of morethan correctly

CoAlgFormula.ml

@@ -628,7 +628,7 @@ and nnf f =
       if n = 0 then TRUE
       else
         let ft = nnf f1 in
-        MORETHAN (n-1,s,f1)
+        MORETHAN (n-1,s,ft)
   | MAX (n, s, f1) ->
       let ft = nnfNeg f1 in
       MAXEXCEPT (n,s, ft)