P.S. If you have F_INV value only in P_MATERIAL=NA you can combine first and second loop:
*XDIM_MEMBERSET P_MATERIAL=BAS(All_MAT)
*XDIM_MEMBERSET FLOW = F_130,F_410,F_INV
*WHEN FLOW
*IS F_INV
*REC(EXPRESSION=-%VALUE%,FLOW=F_120,P_MATERIAL=NA) //store "-F_INV"
*ELSE
*REC(EXPRESSION=%VALUE%,FLOW=F_120,P_MATERIAL=NA) //store sum of F_130,F_410
*ENDWHEN
Negative F_INV on NA will be accumulated with F_130,F_410 for All_MAT
Vadim