(VAR X X1 X2 Y Z )
(RULES 
        a__2nd(cons(X, cons(Y, Z))) -> mark(Y)
        a__from(X) -> cons(mark(X), from(s(X)))
        mark(2nd(X)) -> a__2nd(mark(X))
        mark(from(X)) -> a__from(mark(X))
        mark(cons(X1, X2)) -> cons(mark(X1), X2)
        mark(s(X)) -> s(mark(X))
        a__2nd(X) -> 2nd(X)
        a__from(X) -> from(X)
        
)