Chess Board
[ECO code D02]
TRANSPOSITION
QP. GAME (to Colle Sys.) to QGD SLAV DEF. (Main)
Black's QBP set on QB3(c6) freed the Q-side for his queen, likely seeking a form of QGD, Slav Defence.
White transposes into the Slav Defence of the Queen's Gambit Declined by advancing a gambit (ie. undefended) Queen's Bishop's Pawn to QB4(c4) hoping to entice Black's QP off-centre. W-Alt. 
    White  Black    Transp.White Black
 1. P-Q4   P-Q4		  (1.)
 2. Kt-KB3 P-QB3    (2.	P-QB4  P-QB3)
 3. P-B4	    (3.	Kt-KB3	    )
Continue: Transpose or Undo or Jump or Clear