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1.e4 c5 2.c3 Nf6 3.e5 Nd5
According to some databases I have looked at 4. Nf3 is clearly better than 4. d4. Actually d4 loses more than it wins. For example the lichess.org masters databases scores 4. d4 as 26/43/31 (%wins / %draws / %losses), in contrast to the score of 29/48/23 for 4. Nf3. If I understand it right, there could be some weaker move down the main line after 4. d4 that is responsible for this, but I couldn't find one. It looks like d4 really is not so good for white. Does it mean that 4. Nf3 will gradually become the main line?