W ->X and W->Y mean W can determine X uniquely and W can determine Y uniquely, respectively.

Closure set of W will be {W,X,Y}

Closure set of X will be {X}

Closure set of Y will be{Y}

Example:-

W ->X and W->Y means this:-

W X Y

a1 b1 c1

a2 b1 c2

a1 b1 c1

It doesnt satisfy X->Y