00334nam a2200109 a 450000500170000002000180001708200180003510000200005324500860007326000440015930000210020320251203111553.0  a9780486450780  a515.3523bLAV  aLavrent'ev, M.A  aVariational methods for boundary value problems for systems of elliptic equations  aNew YorkbDover Publications, Incc1989  a153p.c22cm.bHB