f
x
y
cond
and
isNat
x
isNat
y
x
y
cond
tt
x
y
f
s
x
s
y
isNat
s
x
isNat
x
isNat
0
tt
and
tt
tt
tt
and
ff
x
ff
and
x
ff
ff
2.2
isNat
s
x
isNat
x
f
x
y
isNat
y
f
x
y
isNat
x
f
x
y
cond
and
isNat
x
isNat
y
x
y
cond
tt
x
y
f
s
x
s
y
f
x
y
and
isNat
x
isNat
y
true
cond
tt
x
y
f
s
x
s
y
f
x
y
cond
and
isNat
x
isNat
y
x
y
true
Failed!
NaTT
certifiable-1.6