Combinatorists do it discretely. Algebraists do it in groups. Algebraists do it in a ring. Analysts do it continuously. Real analysts do it almost everywhere.
Pure mathematicians do it rigorously.
Topologists do it openly. Topologists do it on rubber sheets. Mathematicians do it forever if they can do one and can do one more. Cantor did it diagonally. Fermat tried to do it in the margin, but couldn't fit it in.