# cap

In mathematics, a cap is the symbol ∩, used to denote the intersection between two sets. Thus the intersection between sets P and Q is written as P ∩ Q. This is illustrated in a Venn diagram as the region of overlap between two sets.

The cap was first used as the symbol for intersection by Guiseppe Peano in *Calcolo Geometrico secondo l'Ausdehnungslehre di H. Grassmann* (1888). See also union.