(VAR x y )
(STRATEGY INNERMOST)
(RULES 
        merge(x,nil) -> x
        merge(nil,y) -> y
        merge(++(x,y),++(u,v)) -> ++(x,merge(y,++(u,v)))
        merge(++(x,y),++(u,v)) -> ++(u,merge(++(x,y),v))
        
)