Is x--->y a trivial functional dependency ?

Question

If y is a subset of x then x-->y is trivial functional dependency(it is well known).But i have doubt: y is not subset of x and x U y = R, then can i say x-->y is a trivial functional dependency.( I read it in some article)

Adding to above question: Why X U Y = R holds in case of multivalued dependencies(trivial).Can somebody give an example so that i can understand.

Answer 1

No, you can't. Suppose R is {a1, a2} x is a1 and y is a2. x U y = R holds, but x-->y is not necessarily true.