This is my sandbox. It's just for experiment, so change it if you want.
def ML_IsInAlphabeth(token):
if token in ['and', 'or', 'not', 'imp', 'iff', 'fls', ')', '(', 'forall', 'exists']:
return True
if token[0]=='x':
if token[1:].isdigit():
return True
return False
def ML_IsMadeOfLetter(s):
char_list = s.split()
if char_list==[]:
return False
for char in char_list:
if not ML_IsInAlphabeth(char):
return False
return True