(VAR X X1 X2 )
(RULES 
        a__h(X) -> a__g(mark(X), X)
        a__g(a, X) -> a__f(b, X)
        a__f(X, X) -> a__h(a__a)
        a__a -> b
        mark(h(X)) -> a__h(mark(X))
        mark(g(X1, X2)) -> a__g(mark(X1), X2)
        mark(a) -> a__a
        mark(f(X1, X2)) -> a__f(mark(X1), X2)
        mark(b) -> b
        a__h(X) -> h(X)
        a__g(X1, X2) -> g(X1, X2)
        a__a -> a
        a__f(X1, X2) -> f(X1, X2)
        
)