def sub(self, x, v): raise SubException("Pred")
def sub(self, x, v): raise SubException("And")
def sub(self, x, v): raise SubException("Exists")
def sub(self, x, v): raise SubException("Forall")
def sub(self, x, v): raise SubException("Var")
def sub(self, x, v): raise SubException("Lit")
def sub(self, x, v): raise SubException("Arrow")