[CHÂTEAU DE LA MUETTE] [Sébastien and Jean-Baptiste ÉRARD (1752-1831 and 1749-1826) musical instrument makers]. Printed: Bulletin des Lois de la République No. 206, [1798] (Paris, Imprimerie de la République); in-8 (small marginal worm gallery). Among various laws, a decree of the Executive Directory of 7 prairial VI (26 May 1798) "proclaims a patent of invention granted to the Cens Érard frères, fabricans d'instrumens de musique", located on rue du Mail, "for the purpose of building and selling, throughout the Republic, harps of a new form, of which they are the inventors"... We join : - A schoolboy notebook cover from the series Les Grands Ouvriers Français, with the portrait and biography of Sébastien Érard.