Diamond operator

This article is about ⋄. For <> following a type name in the Java programming language, see Generics in Java § Diamond operator.

In number theory, the diamond operators 〈d〉 are operators acting on the space of modular forms for the group Γ₁(N), given by the action of a matrix (^{a b}
_{c δ}) in Γ₀(N) where δ ≈ d mod N. The diamond operators form an abelian group and commute with the Hecke operators.

Unicode

In Unicode, the diamond operator is represented by the character U+22C4 ⋄ DIAMOND OPERATOR.^[1]