(VAR x y )
(RULES 
        c(c(c(a(x, y)))) -> b(c(c(c(c(y)))), x)
        c(c(b(c(y), 0))) -> a(0, c(c(a(y, 0))))
        c(c(a(a(y, 0), x))) -> c(y)
        
)