Hecke Algebras and K–Theory
Let R ⊂ P be a reduced (not necessarily finite) root system as defined, e.g., in 3.1.22. There is a slight difference with 3.1.22, since now we are working with lattices instead of vector spaces. This makes axiom 3.1.22(3) superfluous. Thus it is assumed only that, in addition to the above data, a subset R v ⊂ P v, called the dual root system, and a specified bijection R ↔ R v, α ↔ ᾰ are given such that the following three properties hold.