1. e2e4  1... c7c6  2. d2d4  2... d7d5  3. e4d5  3... c6d5  4. f1d3 Fifty years ago R. Fischer revived  this line in his games versus the former world champion T. Petrosian. The  Carlsbad pawn chain is extremely popular nowadays, namely thanks to the  rise of the closed systems like the London one. 4... g8f6 