boolean
implication
(
boolean
a
,
boolean
b
)
return
not
(
a
and
not
b
)
print
strval
(
implication
(
false
,
false
))
print
strval
(
implication
(
true
,
false
))
print
strval
(
implication
(
false
,
true
))
print
strval
(
implication
(
true
,
true
))