When you unpack a weak existential type repeatedly, every time you get a fresh new type. When you unpack a strong existential repeatedly, you always get the sam

When you unpack a weak existential type repeatedly, every time you get a fresh new type. When you unpack a strong existential repeatedly, you always get the same type. Anyway, my original comment was wrong: in ML, every time you project a type component from a module, you always get the same type. So it's more like a strong existential. My bad.