add
true
x
xs
add
and
isNat
x
isList
xs
x
Cons
x
xs
isList
Cons
x
xs
isList
xs
isList
nil
true
isNat
s
x
isNat
x
isNat
0
true
if
true
x
y
x
if
false
x
y
y
and
true
true
true
and
false
x
false
and
x
false
false
2.2
add
true
x
xs
add
and
isNat
x
isList
xs
x
Cons
x
xs
isNat
s
x
isNat
x
add
true
x
xs
isList
xs
add
true
x
xs
and
isNat
x
isList
xs
isList
Cons
x
xs
isList
xs
add
true
x
xs
isNat
x
true
add
true
x
xs
add
and
isNat
x
isList
xs
x
Cons
x
xs
true
Failed!
NaTT
certifiable-1.6