MAYBE

Problem:
 active(__(__(X,Y),Z)) -> mark(__(X,__(Y,Z)))
 active(__(X,nil())) -> mark(X)
 active(__(nil(),X)) -> mark(X)
 active(U11(tt())) -> mark(tt())
 active(U21(tt(),V2)) -> mark(U22(isList(V2)))
 active(U22(tt())) -> mark(tt())
 active(U31(tt())) -> mark(tt())
 active(U41(tt(),V2)) -> mark(U42(isNeList(V2)))
 active(U42(tt())) -> mark(tt())
 active(U51(tt(),V2)) -> mark(U52(isList(V2)))
 active(U52(tt())) -> mark(tt())
 active(U61(tt())) -> mark(tt())
 active(U71(tt(),P)) -> mark(U72(isPal(P)))
 active(U72(tt())) -> mark(tt())
 active(U81(tt())) -> mark(tt())
 active(isList(V)) -> mark(U11(isNeList(V)))
 active(isList(nil())) -> mark(tt())
 active(isList(__(V1,V2))) -> mark(U21(isList(V1),V2))
 active(isNeList(V)) -> mark(U31(isQid(V)))
 active(isNeList(__(V1,V2))) -> mark(U41(isList(V1),V2))
 active(isNeList(__(V1,V2))) -> mark(U51(isNeList(V1),V2))
 active(isNePal(V)) -> mark(U61(isQid(V)))
 active(isNePal(__(I,__(P,I)))) -> mark(U71(isQid(I),P))
 active(isPal(V)) -> mark(U81(isNePal(V)))
 active(isPal(nil())) -> mark(tt())
 active(isQid(a())) -> mark(tt())
 active(isQid(e())) -> mark(tt())
 active(isQid(i())) -> mark(tt())
 active(isQid(o())) -> mark(tt())
 active(isQid(u())) -> mark(tt())
 mark(__(X1,X2)) -> active(__(mark(X1),mark(X2)))
 mark(nil()) -> active(nil())
 mark(U11(X)) -> active(U11(mark(X)))
 mark(tt()) -> active(tt())
 mark(U21(X1,X2)) -> active(U21(mark(X1),X2))
 mark(U22(X)) -> active(U22(mark(X)))
 mark(isList(X)) -> active(isList(X))
 mark(U31(X)) -> active(U31(mark(X)))
 mark(U41(X1,X2)) -> active(U41(mark(X1),X2))
 mark(U42(X)) -> active(U42(mark(X)))
 mark(isNeList(X)) -> active(isNeList(X))
 mark(U51(X1,X2)) -> active(U51(mark(X1),X2))
 mark(U52(X)) -> active(U52(mark(X)))
 mark(U61(X)) -> active(U61(mark(X)))
 mark(U71(X1,X2)) -> active(U71(mark(X1),X2))
 mark(U72(X)) -> active(U72(mark(X)))
 mark(isPal(X)) -> active(isPal(X))
 mark(U81(X)) -> active(U81(mark(X)))
 mark(isQid(X)) -> active(isQid(X))
 mark(isNePal(X)) -> active(isNePal(X))
 mark(a()) -> active(a())
 mark(e()) -> active(e())
 mark(i()) -> active(i())
 mark(o()) -> active(o())
 mark(u()) -> active(u())
 __(mark(X1),X2) -> __(X1,X2)
 __(X1,mark(X2)) -> __(X1,X2)
 __(active(X1),X2) -> __(X1,X2)
 __(X1,active(X2)) -> __(X1,X2)
 U11(mark(X)) -> U11(X)
 U11(active(X)) -> U11(X)
 U21(mark(X1),X2) -> U21(X1,X2)
 U21(X1,mark(X2)) -> U21(X1,X2)
 U21(active(X1),X2) -> U21(X1,X2)
 U21(X1,active(X2)) -> U21(X1,X2)
 U22(mark(X)) -> U22(X)
 U22(active(X)) -> U22(X)
 isList(mark(X)) -> isList(X)
 isList(active(X)) -> isList(X)
 U31(mark(X)) -> U31(X)
 U31(active(X)) -> U31(X)
 U41(mark(X1),X2) -> U41(X1,X2)
 U41(X1,mark(X2)) -> U41(X1,X2)
 U41(active(X1),X2) -> U41(X1,X2)
 U41(X1,active(X2)) -> U41(X1,X2)
 U42(mark(X)) -> U42(X)
 U42(active(X)) -> U42(X)
 isNeList(mark(X)) -> isNeList(X)
 isNeList(active(X)) -> isNeList(X)
 U51(mark(X1),X2) -> U51(X1,X2)
 U51(X1,mark(X2)) -> U51(X1,X2)
 U51(active(X1),X2) -> U51(X1,X2)
 U51(X1,active(X2)) -> U51(X1,X2)
 U52(mark(X)) -> U52(X)
 U52(active(X)) -> U52(X)
 U61(mark(X)) -> U61(X)
 U61(active(X)) -> U61(X)
 U71(mark(X1),X2) -> U71(X1,X2)
 U71(X1,mark(X2)) -> U71(X1,X2)
 U71(active(X1),X2) -> U71(X1,X2)
 U71(X1,active(X2)) -> U71(X1,X2)
 U72(mark(X)) -> U72(X)
 U72(active(X)) -> U72(X)
 isPal(mark(X)) -> isPal(X)
 isPal(active(X)) -> isPal(X)
 U81(mark(X)) -> U81(X)
 U81(active(X)) -> U81(X)
 isQid(mark(X)) -> isQid(X)
 isQid(active(X)) -> isQid(X)
 isNePal(mark(X)) -> isNePal(X)
 isNePal(active(X)) -> isNePal(X)

Proof:
 Open