I don't follow you he

If a2 had more than 2 dimensions then I'd want
a3(vcount,1) = a1(i,1) & a1(i,2) & a2(i,2) & a2(i,n-1)
a3(vcount,2) = a2(i,n)

The number of dimensions refers to the number of subscripts inside the
parentheses, not to the upper or lower bounds of those subscripts. In your
example, a2 is a two-dim array.