This is considered to be the main line of the 4.g3 variation. White has many ways to protect the c-pawn, and Pragg goes for the classical one.
1. d2d4  1... g8f6  2. c2c4  2... e7e6  3. g1f3  3... b7b6 Durarbayli decided to defend with the Queen's Indian Defense, a solid and flexible choice for this important match. 4. g2g3 