White Queen is an overloaded piece. Black Bishop attacks the Knight ( c3 ) , Black Knight attacks the Rook ( e3 ) . After the Queen sacrifice of Black 21 ... Qc2
if 22. QxQ Nxe3 White Queen , Rook and King are forked. But 22. Re2 will not prevent to be forked.
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After Bb7 Black Rook is overloaded. Black Rook protects the Bishop ( c1 ) and prevents to be checkmated after Rd8.
If Rook continues to protect the Bishop after the move Rc7 , White will checkmate after Rd8.
If The Rook didn't leave the back-rank , Bishop will be captures after by the White Rook.
Tactics trainer -- Other tactics