According to Macroeconomics, by Dornbusch,

Disposable income YD=Y-TA+TR, where TA is taxes, TR is transfer payments. This is easy to understand

But later he says

Income Y=C+S+TA-TR, and aggregate demand Y=C+I+G+NX, so I=S+(TA-TR-G)-NX.

this is so weird. if Y=C+S+TA-TR, as YD=Y-TA+TR, then YD=C+S+TA-TR-TA+TR=C+S. This is obviously unreasonable.

DASHEN plz help me!!~~~~