The ``union'' operator can be applied to vectors, to produce a set of vectors. In particular, one can express a nondeterministic choice between the vectors [0,1] and [1,0] by writing
[0,1] union [1,0]
Note that the following is not legal, however:
{[0,1], [1,0]}
As with other operators, vectors are padded with zeros to the same
length before the union operator is applied. The ``in'' operator may also be applied
to vector sets. In general:
[a,b] in ([c,d] union [e,f])
is equivalent to
([a,b] = [c,d]) | ([a,b] = [e,f])