how one can show that a set is not empty?
I ask because I have to checking sets as they are vector subspaces and one of the rules for subspaces are that they are don't the empty set, but how to show that?
hmm, yes but is this adequate for the proof? I mean it is clear that every set has as element the empty set but how to show that there are others which are not the empty set?
The hole problem is that I don't have a specified set. I only have:
Let U be a subset of a vector space. Ist the set a times U a vector subspace? a are elements of a field.
I have no concrete things.