let
rec
f
'
1
=
λ
f
2
. λ
f
3
. λ
x
.
let
f
1
=
f
'
1
f
2
f
3
in
a
1
in
let
rec
f
'
2
=
λ
f
3
. λ
x
.
let
f
2
=
f
'
2
f
3
in
let
f
1
=
f
'
1
f
2
f
3
in
a
2
in
let
rec
f
'
3
=
λ
x
.
let
f
3
=
f
'
3
in
let
f
2
=
f
'
2
f
3
in
let
f
1
=
f
'
1
f
2
f
3
in
a
3
in
a