(VAR X)
(RULES 
a__g(X) -> a__h(X)
a__c -> d
a__h(d) -> a__g(c)
mark(g(X)) -> a__g(X)
mark(h(X)) -> a__h(X)
mark(c) -> a__c
mark(d) -> d
a__g(X) -> g(X)
a__h(X) -> h(X)
a__c -> c
)