CONVENTION OF 27 SEPTEMBER 1968 - JUDGMENT OBTAINED IN A MEMBER STATE - ENFORCEMENT IN ANOTHER CONTRACTING STATE POSSIBLE BY VIRTUE OF ARTICLE 31 OF THE CONVENTION - APPLICATION CONCERNING THE SAME SUBJECT-MATTER AND BETWEEN THE SAME PARTIES BROUGHT BEFORE A COURT OF THAT STATE - PROHIBITION - COSTS OF PROCEDURE ( CONVENTION OF 27 SEPTEMBER 1968 , ART . 31 )