“…The use of mixed and hybrid methods for the approximate solution of source problems has received considerable attention. We mention the works of Herrmann [20], [21], Glowinski [19], Miyoshi [29], Oden [33], Johnson [25], Mercier [27], Ciarlet-Raviart [10], Brezzi [6], [7], Scholz [42], [43], BrezziRaviart [8], Oden-Reddy [35], Raviart-Thomas [40], [41], Falk [14], Falk-Osborn [15], Rannacher [39], and Babuska-Osborn-Pitkäranta [5].…”