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A small right-angle bracket in a square diagram's corner, marking a fibre product.
Also known as: Pullback square mark, Fibre product mark, Corner in a diagram
The little corner drawn inside a commutative square says the square is a pullback — the top-left object is the universal one making it commute. Without the corner the square asserts only that two paths agree; with it, the square asserts a construction.
Marks a commutative square as a pullback: the corner object is the fibre product of the two maps into the shared target.
Contexts: Mathematics
Is placed at the corner nearest the universal object, which is how a reader tells a pullback from a pushout drawn the same way.
Contexts: Mathematics
Two short straight strokes meeting at a right angle, drawn small inside the corner of a larger square of arrows.