29It should be noted first of all that the general implementing rules adopted under the first paragraph of Article 110 of the Staff Regulations may lay down criteria capable of guiding the administration in the exercise of its discretionary power or explain more fully the scope of provisions of the Staff Regulations which are not wholly clear. However, they cannot, by way of explaining more fully a clear term of the Staff Regulations, reduce the scope of those regulations (see the judgments in Case 110/63Willame v Commission [1965] ECR 649, and in Brandau, cited above, and the judgment of the Court of First Instance in Case T-44/89Gouvras-Laycockv Commission [1990] ECR II-217).