isList
nil
tt
isList
Cons
x
xs
isList
xs
downfrom
0
nil
downfrom
s
x
Cons
s
x
downfrom
x
f
x
cond
isList
downfrom
x
s
x
cond
tt
x
f
x
2.2
cond
tt
x
f
x
downfrom
s
x
downfrom
x
f
x
downfrom
x
f
x
cond
isList
downfrom
x
s
x
isList
Cons
x
xs
isList
xs
f
x
isList
downfrom
x
true
f
x
cond
isList
downfrom
x
s
x
cond
tt
x
f
x
true
Failed!
NaTT
certifiable-1.6