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1.Nf3 c5 2.e3 g6 3.d4 Bg7 4.dxc5 Qa5+ · ECO A04
Colle System: Rhamphorhynchus Variation is a chess opening that arises after 1.Nf3 c5 2.e3 g6 3.d4 Bg7 4.dxc5 Qa5+. It is classified A04 in the ECO system, and the position after these moves has white to move.
This line is a variation within the Colle System family. The strategic ideas above describe the family as a whole; this particular line reaches them by the move order 1.Nf3 c5 2.e3 g6 3.d4 Bg7 4.dxc5 Qa5+.