[EN] SOLID FORMS COMPRISING 4-AMINO-I-&bgr;-D-RIBOFURANOSYL-1,3,5-TRIAZIN-2(1H)-ONE AND A COFORMER, COMPOSITIONS AND METHODS OF USE THEREOF [FR] FORMES SOLIDES COMPRENANT DE LA 4-AMINO-1-&bgr;-D-RIBOFURANOSYL-1,3,5-TRIAZIN-2(1H)-ONE ET UN CO-AGENT DE FORMATION, COMPOSITIONS ET LEURS PROCÉDÉS D'UTILISATION