Hey everyone, I am integrating something (specifically 2-forms, but I think this is a general statement) over a set B of (real) codimension 2 in a 4-manifold (CP_2). I've been told that the measure of a set of codimension 2 will vanish, but I don't really understand why. I've been thinking about exterior products and hodge duals but I can't seem to understand it from that direction. Does anyone have any insights? Thanks!