1.Sa6 +! Kd7 2.Qf8 LEh2! (2...LENg2?) 3.Na7 d1=N 4.Bb5 + Nxb5 # 1.Sc6 +! Kf7 2.Qh8 LEg2! (2.LEh2?) 3.Ba6 f1=B 4.Nb5 + Bxb5 # Themes: Masced white Dentist combined with Umnov-theme + Bivalve, double unpin of white N and B, ambush moves of LEg1 which forces control over 2nd horizontal and determines Bivalve-theme in play of black Pawns. Anti-dual moves by LEg1, critical moves by unpined white N and B. An interesting play demonstrates white S/Q battery - after moves of forward piece Sb8 and the black King we have double line-opening for the whiteQueen!