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