(VAR x y z )
(RULES 
        msort(nil) -> nil
        msort(.(x, y)) -> .(min(x, y), msort(del(min(x, y), .(x, y))))
        min(x, nil) -> x
        min(x, .(y, z)) -> if(<=(x, y), min(x, z), min(y, z))
        del(x, nil) -> nil
        del(x, .(y, z)) -> if(=(x, y), z, .(y, del(x, z)))
        
)