No, because all {x, y, z}s are {x, y}s, but the opposite is not true. Said differently, any function that applies to the general {x, y} also applies to the mor

No, because all {x, y, z}s are {x, y}s, but the opposite is not true. Said differently, any function that applies to the general {x, y} also applies to the more specific {x, y, z} (it will just not use the z part) but a function that requires a {x, y, z} specifically will not work with all {x, y}s.