foldl
x
Cons
S
0
xs
foldl
S
x
xs
foldl
S
0
Cons
x
xs
foldl
S
x
xs
foldr
a
Cons
x
xs
op
x
foldr
a
xs
foldr
a
Nil
a
foldl
a
Nil
a
notEmpty
Cons
x
xs
True
notEmpty
Nil
False
op
x
S
0
S
x
op
S
0
y
S
y
fold
a
xs
Cons
foldl
a
xs
Cons
foldr
a
xs
Nil
foldl
2
Cons
2
S
1
0
0
foldr
2
op
2
Nil
0
notEmpty
1
True
0
False
0
fold
2
INNERMOST