A Gerstenhaber algebra is a graded-commutative algebra with a Lie bracket of degree −1 satisfying the Poisson identity. Everything is understood to satisfy the usual superalgebra sign conventions. More precisely, the algebra has two products, one written as ordinary multiplication and one written as [,], and a Z -grading called degree (in theoretical physics sometimes called ghost number). The degree of an element a is denoted by | a |. These satisfy the identities