This move is quite flexible. White may intend an early d2-d4, with transposition to a
normal queen pawn opening. An early c2-c4 could make the game an English. g2-g3
or b2-b3 often leads to reversed openings, known as the King's Indian Attack and
Larsen-Nimzovich Attack respectively.
After 1...d5, 2.c4 was developed and played by Richard Reti. This flank
system had a profound influence on chess understanding: it is sometimes possible
to control the center of the board without occupying it with pawns!
