COMMENTS ON GEPNER MODELS AND TYPE-I VACUA IN STRING THEORY

We construct open descendants of Gepner models, concentrating mainly o n the six-dimensional case, where they give type I vacua with rich pat terns of Chan-Paton symmetry breaking and various numbers of tensor mu ltiplets, including zero. We also relate the models in D < 10 without open sectors, recently found by other authors, to the generalized Klei n-bottle projections allowed by the crosscap constraint.