D + R -> DR
DR -> D + R
DR + G_GDP -> DRG_GDP
DRG_GDP -> DR + G_GDP
DRG_GDP -> DRG + GDP
DRG + GDP -> DRG_GDP
DRG + GTP -> DRG_GTP
DRG_GTP -> DRG + GTP
DRG_GTP -> DR + G_GTP
G_GTP -> G_GDP