Miguel R. Penabad Nieves R. Brisaboa José R. Paramá Hendrik Decker A General Procedure to Test Containment of Conjunctive Queries. 1-10 2001 INAP http://www.ifcomputer.com/inap/inap2001/program/ddlp_penabad.ps db/conf/inap/inap2001.html#PenabadBPD01