Protecting the e5-pawn.
1. g1f3  1... g8f6  2. b2b3  2... c7c5  3. c1b2  3... b8c6  4. e2e3  4... g7g6  5. b1c3 [%c_effect c3;square;c3;type;Interesting;persistent;true] A creative move with the idea of exploiting the pin on the a1-h8 diagonal and playing Nd5 or Ne4 next. 5... e7e5 [%c_effect e5;square;e5;type;Interesting;persistent;true] A novelty already on move five. 6. f1b5 