Lattices and Root Bases
François R. Cossec, Igor Vladimirovich Dolgachev · Progress in mathematics · 1989
A lattice is a free abelian group M of finite rank rk(M) equipped with a symmetric bilinear form ϕ:MxM → Z . The value of this form on a pair (x,y)∈MxM will be denoted by x•y. We write x 2 to denote x•x.