411 REFERENCE · Wikibooks
Chess Opening Theory/1. b4/1...e6/2. Bb2/2...Nf6/3. b5/3...a6/4. a4/4...axb5/5. axb5
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Polish Opening: Queenside Defence
5. axb5
White recaptures on b5. With their rook on a8 threatened, Black should play /5...Rxa1/, trading the rooks.