Note on the residual finiteness of Artin groups

Let A be an Artin group. A partition P of the set of standard generators of A is called admissible if, for all X; Y is an element of P, X not equal Y, there is at most one pair (s, t) is an element of X x Y which has a relation. An admissible partition P determines a quotient Coxeter graph Gamma= P. We prove that, if Gamma= P is either a forest or an even triangle free Coxeter graph and A(X) is residually finite for all X is an element of P, then A is residually finite.