g1(A) -> A
g1(B) -> A
g1(B) -> B
g1(C) -> A
g1(C) -> B
g1(C) -> C
foldB2(t, 0) -> t
foldB2(t, s1(n)) -> f2(foldB2(t, n), B)
foldC2(t, 0) -> t
foldC2(t, s1(n)) -> f2(foldC2(t, n), C)
f2(t, x) -> f'2(t, g1(x))
f'2(triple3(a, b, c), C) -> triple3(a, b, s1(c))
f'2(triple3(a, b, c), B) -> f2(triple3(a, b, c), A)
f'2(triple3(a, b, c), A) -> f''1(foldB2(triple3(s1(a), 0, c), b))
f''1(triple3(a, b, c)) -> foldC2(triple3(a, b, 0), c)
fold3(t, x, 0) -> t
fold3(t, x, s1(n)) -> f2(fold3(t, x, n), x)
↳ QTRS
↳ DependencyPairsProof
g1(A) -> A
g1(B) -> A
g1(B) -> B
g1(C) -> A
g1(C) -> B
g1(C) -> C
foldB2(t, 0) -> t
foldB2(t, s1(n)) -> f2(foldB2(t, n), B)
foldC2(t, 0) -> t
foldC2(t, s1(n)) -> f2(foldC2(t, n), C)
f2(t, x) -> f'2(t, g1(x))
f'2(triple3(a, b, c), C) -> triple3(a, b, s1(c))
f'2(triple3(a, b, c), B) -> f2(triple3(a, b, c), A)
f'2(triple3(a, b, c), A) -> f''1(foldB2(triple3(s1(a), 0, c), b))
f''1(triple3(a, b, c)) -> foldC2(triple3(a, b, 0), c)
fold3(t, x, 0) -> t
fold3(t, x, s1(n)) -> f2(fold3(t, x, n), x)
F'2(triple3(a, b, c), A) -> FOLDB2(triple3(s1(a), 0, c), b)
FOLD3(t, x, s1(n)) -> FOLD3(t, x, n)
FOLD3(t, x, s1(n)) -> F2(fold3(t, x, n), x)
F2(t, x) -> F'2(t, g1(x))
FOLDC2(t, s1(n)) -> F2(foldC2(t, n), C)
F2(t, x) -> G1(x)
FOLDB2(t, s1(n)) -> FOLDB2(t, n)
F''1(triple3(a, b, c)) -> FOLDC2(triple3(a, b, 0), c)
FOLDC2(t, s1(n)) -> FOLDC2(t, n)
F'2(triple3(a, b, c), A) -> F''1(foldB2(triple3(s1(a), 0, c), b))
F'2(triple3(a, b, c), B) -> F2(triple3(a, b, c), A)
FOLDB2(t, s1(n)) -> F2(foldB2(t, n), B)
g1(A) -> A
g1(B) -> A
g1(B) -> B
g1(C) -> A
g1(C) -> B
g1(C) -> C
foldB2(t, 0) -> t
foldB2(t, s1(n)) -> f2(foldB2(t, n), B)
foldC2(t, 0) -> t
foldC2(t, s1(n)) -> f2(foldC2(t, n), C)
f2(t, x) -> f'2(t, g1(x))
f'2(triple3(a, b, c), C) -> triple3(a, b, s1(c))
f'2(triple3(a, b, c), B) -> f2(triple3(a, b, c), A)
f'2(triple3(a, b, c), A) -> f''1(foldB2(triple3(s1(a), 0, c), b))
f''1(triple3(a, b, c)) -> foldC2(triple3(a, b, 0), c)
fold3(t, x, 0) -> t
fold3(t, x, s1(n)) -> f2(fold3(t, x, n), x)
↳ QTRS
↳ DependencyPairsProof
↳ QDP
↳ DependencyGraphProof
F'2(triple3(a, b, c), A) -> FOLDB2(triple3(s1(a), 0, c), b)
FOLD3(t, x, s1(n)) -> FOLD3(t, x, n)
FOLD3(t, x, s1(n)) -> F2(fold3(t, x, n), x)
F2(t, x) -> F'2(t, g1(x))
FOLDC2(t, s1(n)) -> F2(foldC2(t, n), C)
F2(t, x) -> G1(x)
FOLDB2(t, s1(n)) -> FOLDB2(t, n)
F''1(triple3(a, b, c)) -> FOLDC2(triple3(a, b, 0), c)
FOLDC2(t, s1(n)) -> FOLDC2(t, n)
F'2(triple3(a, b, c), A) -> F''1(foldB2(triple3(s1(a), 0, c), b))
F'2(triple3(a, b, c), B) -> F2(triple3(a, b, c), A)
FOLDB2(t, s1(n)) -> F2(foldB2(t, n), B)
g1(A) -> A
g1(B) -> A
g1(B) -> B
g1(C) -> A
g1(C) -> B
g1(C) -> C
foldB2(t, 0) -> t
foldB2(t, s1(n)) -> f2(foldB2(t, n), B)
foldC2(t, 0) -> t
foldC2(t, s1(n)) -> f2(foldC2(t, n), C)
f2(t, x) -> f'2(t, g1(x))
f'2(triple3(a, b, c), C) -> triple3(a, b, s1(c))
f'2(triple3(a, b, c), B) -> f2(triple3(a, b, c), A)
f'2(triple3(a, b, c), A) -> f''1(foldB2(triple3(s1(a), 0, c), b))
f''1(triple3(a, b, c)) -> foldC2(triple3(a, b, 0), c)
fold3(t, x, 0) -> t
fold3(t, x, s1(n)) -> f2(fold3(t, x, n), x)
↳ QTRS
↳ DependencyPairsProof
↳ QDP
↳ DependencyGraphProof
↳ AND
↳ QDP
↳ QDPOrderProof
↳ QDP
F'2(triple3(a, b, c), A) -> FOLDB2(triple3(s1(a), 0, c), b)
F2(t, x) -> F'2(t, g1(x))
FOLDC2(t, s1(n)) -> F2(foldC2(t, n), C)
FOLDB2(t, s1(n)) -> FOLDB2(t, n)
F''1(triple3(a, b, c)) -> FOLDC2(triple3(a, b, 0), c)
FOLDC2(t, s1(n)) -> FOLDC2(t, n)
F'2(triple3(a, b, c), A) -> F''1(foldB2(triple3(s1(a), 0, c), b))
F'2(triple3(a, b, c), B) -> F2(triple3(a, b, c), A)
FOLDB2(t, s1(n)) -> F2(foldB2(t, n), B)
g1(A) -> A
g1(B) -> A
g1(B) -> B
g1(C) -> A
g1(C) -> B
g1(C) -> C
foldB2(t, 0) -> t
foldB2(t, s1(n)) -> f2(foldB2(t, n), B)
foldC2(t, 0) -> t
foldC2(t, s1(n)) -> f2(foldC2(t, n), C)
f2(t, x) -> f'2(t, g1(x))
f'2(triple3(a, b, c), C) -> triple3(a, b, s1(c))
f'2(triple3(a, b, c), B) -> f2(triple3(a, b, c), A)
f'2(triple3(a, b, c), A) -> f''1(foldB2(triple3(s1(a), 0, c), b))
f''1(triple3(a, b, c)) -> foldC2(triple3(a, b, 0), c)
fold3(t, x, 0) -> t
fold3(t, x, s1(n)) -> f2(fold3(t, x, n), x)
The following pairs can be oriented strictly and are deleted.
The remaining pairs can at least be oriented weakly.
F'2(triple3(a, b, c), A) -> FOLDB2(triple3(s1(a), 0, c), b)
Used ordering: Polynomial Order [17,21] with Interpretation:
F2(t, x) -> F'2(t, g1(x))
FOLDC2(t, s1(n)) -> F2(foldC2(t, n), C)
FOLDB2(t, s1(n)) -> FOLDB2(t, n)
F''1(triple3(a, b, c)) -> FOLDC2(triple3(a, b, 0), c)
FOLDC2(t, s1(n)) -> FOLDC2(t, n)
F'2(triple3(a, b, c), A) -> F''1(foldB2(triple3(s1(a), 0, c), b))
F'2(triple3(a, b, c), B) -> F2(triple3(a, b, c), A)
FOLDB2(t, s1(n)) -> F2(foldB2(t, n), B)
POL( F'2(x1, x2) ) = x1
POL( triple3(x1, ..., x3) ) = x2 + 1
POL( FOLDB2(x1, x2) ) = max{0, x1 + x2 - 1}
POL( 0 ) = 0
POL( F2(x1, x2) ) = x1
POL( FOLDC2(x1, x2) ) = x1
POL( foldC2(x1, x2) ) = x1
POL( s1(x1) ) = x1 + 1
POL( F''1(x1) ) = x1
POL( foldB2(x1, x2) ) = x1
POL( f2(x1, x2) ) = x1
POL( f'2(x1, x2) ) = x1
POL( f''1(x1) ) = x1
foldC2(t, 0) -> t
foldB2(t, s1(n)) -> f2(foldB2(t, n), B)
f''1(triple3(a, b, c)) -> foldC2(triple3(a, b, 0), c)
foldC2(t, s1(n)) -> f2(foldC2(t, n), C)
f'2(triple3(a, b, c), A) -> f''1(foldB2(triple3(s1(a), 0, c), b))
f'2(triple3(a, b, c), B) -> f2(triple3(a, b, c), A)
f2(t, x) -> f'2(t, g1(x))
f'2(triple3(a, b, c), C) -> triple3(a, b, s1(c))
foldB2(t, 0) -> t
↳ QTRS
↳ DependencyPairsProof
↳ QDP
↳ DependencyGraphProof
↳ AND
↳ QDP
↳ QDPOrderProof
↳ QDP
↳ DependencyGraphProof
↳ QDP
F2(t, x) -> F'2(t, g1(x))
FOLDC2(t, s1(n)) -> F2(foldC2(t, n), C)
FOLDB2(t, s1(n)) -> FOLDB2(t, n)
F''1(triple3(a, b, c)) -> FOLDC2(triple3(a, b, 0), c)
FOLDC2(t, s1(n)) -> FOLDC2(t, n)
F'2(triple3(a, b, c), B) -> F2(triple3(a, b, c), A)
F'2(triple3(a, b, c), A) -> F''1(foldB2(triple3(s1(a), 0, c), b))
FOLDB2(t, s1(n)) -> F2(foldB2(t, n), B)
g1(A) -> A
g1(B) -> A
g1(B) -> B
g1(C) -> A
g1(C) -> B
g1(C) -> C
foldB2(t, 0) -> t
foldB2(t, s1(n)) -> f2(foldB2(t, n), B)
foldC2(t, 0) -> t
foldC2(t, s1(n)) -> f2(foldC2(t, n), C)
f2(t, x) -> f'2(t, g1(x))
f'2(triple3(a, b, c), C) -> triple3(a, b, s1(c))
f'2(triple3(a, b, c), B) -> f2(triple3(a, b, c), A)
f'2(triple3(a, b, c), A) -> f''1(foldB2(triple3(s1(a), 0, c), b))
f''1(triple3(a, b, c)) -> foldC2(triple3(a, b, 0), c)
fold3(t, x, 0) -> t
fold3(t, x, s1(n)) -> f2(fold3(t, x, n), x)
↳ QTRS
↳ DependencyPairsProof
↳ QDP
↳ DependencyGraphProof
↳ AND
↳ QDP
↳ QDPOrderProof
↳ QDP
↳ DependencyGraphProof
↳ AND
↳ QDP
↳ QDPOrderProof
↳ QDP
↳ QDP
F2(t, x) -> F'2(t, g1(x))
FOLDC2(t, s1(n)) -> F2(foldC2(t, n), C)
F''1(triple3(a, b, c)) -> FOLDC2(triple3(a, b, 0), c)
FOLDC2(t, s1(n)) -> FOLDC2(t, n)
F'2(triple3(a, b, c), A) -> F''1(foldB2(triple3(s1(a), 0, c), b))
F'2(triple3(a, b, c), B) -> F2(triple3(a, b, c), A)
g1(A) -> A
g1(B) -> A
g1(B) -> B
g1(C) -> A
g1(C) -> B
g1(C) -> C
foldB2(t, 0) -> t
foldB2(t, s1(n)) -> f2(foldB2(t, n), B)
foldC2(t, 0) -> t
foldC2(t, s1(n)) -> f2(foldC2(t, n), C)
f2(t, x) -> f'2(t, g1(x))
f'2(triple3(a, b, c), C) -> triple3(a, b, s1(c))
f'2(triple3(a, b, c), B) -> f2(triple3(a, b, c), A)
f'2(triple3(a, b, c), A) -> f''1(foldB2(triple3(s1(a), 0, c), b))
f''1(triple3(a, b, c)) -> foldC2(triple3(a, b, 0), c)
fold3(t, x, 0) -> t
fold3(t, x, s1(n)) -> f2(fold3(t, x, n), x)
The following pairs can be oriented strictly and are deleted.
The remaining pairs can at least be oriented weakly.
FOLDC2(t, s1(n)) -> F2(foldC2(t, n), C)
FOLDC2(t, s1(n)) -> FOLDC2(t, n)
Used ordering: Polynomial Order [17,21] with Interpretation:
F2(t, x) -> F'2(t, g1(x))
F''1(triple3(a, b, c)) -> FOLDC2(triple3(a, b, 0), c)
F'2(triple3(a, b, c), A) -> F''1(foldB2(triple3(s1(a), 0, c), b))
F'2(triple3(a, b, c), B) -> F2(triple3(a, b, c), A)
POL( FOLDC2(x1, x2) ) = x1 + x2
POL( s1(x1) ) = x1 + 1
POL( F2(x1, x2) ) = x1
POL( foldC2(x1, x2) ) = x1 + x2
POL( F'2(x1, x2) ) = x1
POL( F''1(x1) ) = x1
POL( triple3(x1, ..., x3) ) = x3
POL( 0 ) = 0
POL( foldB2(x1, x2) ) = x1
POL( f2(x1, x2) ) = x1 + x2
POL( C ) = 1
POL( f'2(x1, x2) ) = x1 + x2
POL( g1(x1) ) = x1
POL( A ) = 0
POL( f''1(x1) ) = x1
POL( B ) = 0
g1(B) -> A
foldB2(t, s1(n)) -> f2(foldB2(t, n), B)
f''1(triple3(a, b, c)) -> foldC2(triple3(a, b, 0), c)
foldC2(t, s1(n)) -> f2(foldC2(t, n), C)
f'2(triple3(a, b, c), A) -> f''1(foldB2(triple3(s1(a), 0, c), b))
f'2(triple3(a, b, c), B) -> f2(triple3(a, b, c), A)
f2(t, x) -> f'2(t, g1(x))
g1(C) -> B
f'2(triple3(a, b, c), C) -> triple3(a, b, s1(c))
g1(A) -> A
foldB2(t, 0) -> t
g1(B) -> B
g1(C) -> C
foldC2(t, 0) -> t
g1(C) -> A
↳ QTRS
↳ DependencyPairsProof
↳ QDP
↳ DependencyGraphProof
↳ AND
↳ QDP
↳ QDPOrderProof
↳ QDP
↳ DependencyGraphProof
↳ AND
↳ QDP
↳ QDPOrderProof
↳ QDP
↳ DependencyGraphProof
↳ QDP
↳ QDP
F2(t, x) -> F'2(t, g1(x))
F''1(triple3(a, b, c)) -> FOLDC2(triple3(a, b, 0), c)
F'2(triple3(a, b, c), B) -> F2(triple3(a, b, c), A)
F'2(triple3(a, b, c), A) -> F''1(foldB2(triple3(s1(a), 0, c), b))
g1(A) -> A
g1(B) -> A
g1(B) -> B
g1(C) -> A
g1(C) -> B
g1(C) -> C
foldB2(t, 0) -> t
foldB2(t, s1(n)) -> f2(foldB2(t, n), B)
foldC2(t, 0) -> t
foldC2(t, s1(n)) -> f2(foldC2(t, n), C)
f2(t, x) -> f'2(t, g1(x))
f'2(triple3(a, b, c), C) -> triple3(a, b, s1(c))
f'2(triple3(a, b, c), B) -> f2(triple3(a, b, c), A)
f'2(triple3(a, b, c), A) -> f''1(foldB2(triple3(s1(a), 0, c), b))
f''1(triple3(a, b, c)) -> foldC2(triple3(a, b, 0), c)
fold3(t, x, 0) -> t
fold3(t, x, s1(n)) -> f2(fold3(t, x, n), x)
↳ QTRS
↳ DependencyPairsProof
↳ QDP
↳ DependencyGraphProof
↳ AND
↳ QDP
↳ QDPOrderProof
↳ QDP
↳ DependencyGraphProof
↳ AND
↳ QDP
↳ QDPOrderProof
↳ QDP
↳ DependencyGraphProof
↳ QDP
↳ QDPOrderProof
↳ QDP
↳ QDP
F2(t, x) -> F'2(t, g1(x))
F'2(triple3(a, b, c), B) -> F2(triple3(a, b, c), A)
g1(A) -> A
g1(B) -> A
g1(B) -> B
g1(C) -> A
g1(C) -> B
g1(C) -> C
foldB2(t, 0) -> t
foldB2(t, s1(n)) -> f2(foldB2(t, n), B)
foldC2(t, 0) -> t
foldC2(t, s1(n)) -> f2(foldC2(t, n), C)
f2(t, x) -> f'2(t, g1(x))
f'2(triple3(a, b, c), C) -> triple3(a, b, s1(c))
f'2(triple3(a, b, c), B) -> f2(triple3(a, b, c), A)
f'2(triple3(a, b, c), A) -> f''1(foldB2(triple3(s1(a), 0, c), b))
f''1(triple3(a, b, c)) -> foldC2(triple3(a, b, 0), c)
fold3(t, x, 0) -> t
fold3(t, x, s1(n)) -> f2(fold3(t, x, n), x)
The following pairs can be oriented strictly and are deleted.
The remaining pairs can at least be oriented weakly.
F2(t, x) -> F'2(t, g1(x))
Used ordering: Polynomial Order [17,21] with Interpretation:
F'2(triple3(a, b, c), B) -> F2(triple3(a, b, c), A)
POL( F2(x1, x2) ) = x2 + 1
POL( F'2(x1, x2) ) = x2
POL( g1(x1) ) = x1
POL( B ) = 1
POL( A ) = 0
POL( C ) = 1
g1(B) -> A
g1(C) -> B
g1(A) -> A
g1(B) -> B
g1(C) -> C
g1(C) -> A
↳ QTRS
↳ DependencyPairsProof
↳ QDP
↳ DependencyGraphProof
↳ AND
↳ QDP
↳ QDPOrderProof
↳ QDP
↳ DependencyGraphProof
↳ AND
↳ QDP
↳ QDPOrderProof
↳ QDP
↳ DependencyGraphProof
↳ QDP
↳ QDPOrderProof
↳ QDP
↳ DependencyGraphProof
↳ QDP
↳ QDP
F'2(triple3(a, b, c), B) -> F2(triple3(a, b, c), A)
g1(A) -> A
g1(B) -> A
g1(B) -> B
g1(C) -> A
g1(C) -> B
g1(C) -> C
foldB2(t, 0) -> t
foldB2(t, s1(n)) -> f2(foldB2(t, n), B)
foldC2(t, 0) -> t
foldC2(t, s1(n)) -> f2(foldC2(t, n), C)
f2(t, x) -> f'2(t, g1(x))
f'2(triple3(a, b, c), C) -> triple3(a, b, s1(c))
f'2(triple3(a, b, c), B) -> f2(triple3(a, b, c), A)
f'2(triple3(a, b, c), A) -> f''1(foldB2(triple3(s1(a), 0, c), b))
f''1(triple3(a, b, c)) -> foldC2(triple3(a, b, 0), c)
fold3(t, x, 0) -> t
fold3(t, x, s1(n)) -> f2(fold3(t, x, n), x)
↳ QTRS
↳ DependencyPairsProof
↳ QDP
↳ DependencyGraphProof
↳ AND
↳ QDP
↳ QDPOrderProof
↳ QDP
↳ DependencyGraphProof
↳ AND
↳ QDP
↳ QDP
↳ QDPOrderProof
↳ QDP
FOLDB2(t, s1(n)) -> FOLDB2(t, n)
g1(A) -> A
g1(B) -> A
g1(B) -> B
g1(C) -> A
g1(C) -> B
g1(C) -> C
foldB2(t, 0) -> t
foldB2(t, s1(n)) -> f2(foldB2(t, n), B)
foldC2(t, 0) -> t
foldC2(t, s1(n)) -> f2(foldC2(t, n), C)
f2(t, x) -> f'2(t, g1(x))
f'2(triple3(a, b, c), C) -> triple3(a, b, s1(c))
f'2(triple3(a, b, c), B) -> f2(triple3(a, b, c), A)
f'2(triple3(a, b, c), A) -> f''1(foldB2(triple3(s1(a), 0, c), b))
f''1(triple3(a, b, c)) -> foldC2(triple3(a, b, 0), c)
fold3(t, x, 0) -> t
fold3(t, x, s1(n)) -> f2(fold3(t, x, n), x)
The following pairs can be oriented strictly and are deleted.
The remaining pairs can at least be oriented weakly.
FOLDB2(t, s1(n)) -> FOLDB2(t, n)
POL( FOLDB2(x1, x2) ) = x2
POL( s1(x1) ) = x1 + 1
↳ QTRS
↳ DependencyPairsProof
↳ QDP
↳ DependencyGraphProof
↳ AND
↳ QDP
↳ QDPOrderProof
↳ QDP
↳ DependencyGraphProof
↳ AND
↳ QDP
↳ QDP
↳ QDPOrderProof
↳ QDP
↳ PisEmptyProof
↳ QDP
g1(A) -> A
g1(B) -> A
g1(B) -> B
g1(C) -> A
g1(C) -> B
g1(C) -> C
foldB2(t, 0) -> t
foldB2(t, s1(n)) -> f2(foldB2(t, n), B)
foldC2(t, 0) -> t
foldC2(t, s1(n)) -> f2(foldC2(t, n), C)
f2(t, x) -> f'2(t, g1(x))
f'2(triple3(a, b, c), C) -> triple3(a, b, s1(c))
f'2(triple3(a, b, c), B) -> f2(triple3(a, b, c), A)
f'2(triple3(a, b, c), A) -> f''1(foldB2(triple3(s1(a), 0, c), b))
f''1(triple3(a, b, c)) -> foldC2(triple3(a, b, 0), c)
fold3(t, x, 0) -> t
fold3(t, x, s1(n)) -> f2(fold3(t, x, n), x)
↳ QTRS
↳ DependencyPairsProof
↳ QDP
↳ DependencyGraphProof
↳ AND
↳ QDP
↳ QDP
↳ QDPOrderProof
FOLD3(t, x, s1(n)) -> FOLD3(t, x, n)
g1(A) -> A
g1(B) -> A
g1(B) -> B
g1(C) -> A
g1(C) -> B
g1(C) -> C
foldB2(t, 0) -> t
foldB2(t, s1(n)) -> f2(foldB2(t, n), B)
foldC2(t, 0) -> t
foldC2(t, s1(n)) -> f2(foldC2(t, n), C)
f2(t, x) -> f'2(t, g1(x))
f'2(triple3(a, b, c), C) -> triple3(a, b, s1(c))
f'2(triple3(a, b, c), B) -> f2(triple3(a, b, c), A)
f'2(triple3(a, b, c), A) -> f''1(foldB2(triple3(s1(a), 0, c), b))
f''1(triple3(a, b, c)) -> foldC2(triple3(a, b, 0), c)
fold3(t, x, 0) -> t
fold3(t, x, s1(n)) -> f2(fold3(t, x, n), x)
The following pairs can be oriented strictly and are deleted.
The remaining pairs can at least be oriented weakly.
FOLD3(t, x, s1(n)) -> FOLD3(t, x, n)
POL( FOLD3(x1, ..., x3) ) = x3
POL( s1(x1) ) = x1 + 1
↳ QTRS
↳ DependencyPairsProof
↳ QDP
↳ DependencyGraphProof
↳ AND
↳ QDP
↳ QDP
↳ QDPOrderProof
↳ QDP
↳ PisEmptyProof
g1(A) -> A
g1(B) -> A
g1(B) -> B
g1(C) -> A
g1(C) -> B
g1(C) -> C
foldB2(t, 0) -> t
foldB2(t, s1(n)) -> f2(foldB2(t, n), B)
foldC2(t, 0) -> t
foldC2(t, s1(n)) -> f2(foldC2(t, n), C)
f2(t, x) -> f'2(t, g1(x))
f'2(triple3(a, b, c), C) -> triple3(a, b, s1(c))
f'2(triple3(a, b, c), B) -> f2(triple3(a, b, c), A)
f'2(triple3(a, b, c), A) -> f''1(foldB2(triple3(s1(a), 0, c), b))
f''1(triple3(a, b, c)) -> foldC2(triple3(a, b, 0), c)
fold3(t, x, 0) -> t
fold3(t, x, s1(n)) -> f2(fold3(t, x, n), x)