def empty_is_empty(asker):
return asker.reply(answer=T.yes())
def return_yes(asker):
return asker.reply(answer=T.yes())
def no_to_yes(asker):
return asker.reply(answer=T.yes())
def opposite(a):
if a.head == T.yes.head:
return T.no()
elif a.head == T.no.head:
return T.yes()
return T(opposite.head, a=a)
