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Twin Problem 6: Mate in 2 Moves

(White: Kh4, Qb6, Rb3, Bd6, Ng4, Ng7, a2, g2, Black: Kd5, Ra4, Ba7, b5.)

White to move and mate in 2

Now, replace white knight g4 with white bishop and move white pawn a2 to b2:

(White: Kh4, Qb6, Rb3, Bd6, Bg4, Ng7, b2, g2, Black: Kd5, Ra4, Ba7, b5.)

White to move and mate in 2

Solution:

(a) 1. Rd3+! Kc4 2. Ne5# (1. ... Ke4 2. Nf2#, 1. ... Rd4 2. Rxd4#) 
(b) 1. Rxb5+! Kc4 2. Be2# (1. ... Ke4 2. Bf5#)