CONVENTION ON JURISDICTION AND THE ENFORCEMENT OF JUDGMENTS - AGREEMENT ON JURISDICTION - APPEARANCE ENTERED BY THE DEFENDANT IN THE COURT SEISED - APPEARANCE ENTERED NOT ONLY TO CONTEST THE JURISDICTION BUT ALSO TO PRESENT A DEFENCE ON THE SUBSTANCE - ENTERING AN APPEARANCE DOES NOT ENTAIL SUBMISSION TO THE JURISDICTION ( CONVENTION OF 27 SEPTEMBER 1968 , ART . 18 )