[romwell]

The integral notation is a set-builder in disguise:

∫ f(x) dx = set of solutions of diff. eq. g'(x) = f(x)

Of course, writing

∫ 2x dx = { x² + C | C ∊ R }

grows old pretty fast, so we drop a couple of characters here and there, but it's pretty consistent with set-builder.

Of course, this only goes to show the article's point that what "=" means here requires a lot of context.