Symmetrical subgroups of Artin groups

We show that the subgroup fixed by a group of symmetries of an Artin system (A, S) is itself an Artin group under the hyothesis that the Deligne complex associated to A admits a suitable CAT(0) metric. Such a metric is known to exist For all Artin groups of type FC, which include all the finite type Artin groups as well as many infinite types. We also recover the previously known analogous result for an arbitrary Coxeter system (W, S). (C) 2000 Academic Press.