Reference for a preliminary ruling from the Hoge Raad der Nederlanden by judgment of that court of 30 October 1998 in the case of 1. Assco Gerüste GmbH and 2. R. Van Dijk, trading as Assco Holland Steigers Plettac Nederland, against 1. Wilhelm Layher GmbH & Co and 2. Layher BV (Case C-392/98) (1999/C 1/09)