Hi everyone On page 147 of the note "Group C-Algebras and K-theory" by N.Higson and E.Guentner there are something about the stabilized homotopy category of graded C algebra, which is a category whose objects are the graded C* -algebras and morphisms from A to B are the homotopy classes of graded -homomorphisms from A to $B\otimes K(H)$. But the exact definition of composition of morphisms and the identity morphisms are not mentioned. I think the definition is dual to the defition of amplified category of graded C-algebras, is there someone knows some references about this?\newline Thinks