Hi, there. I am pretty new to GAMS. And I am struggling with following problem.

SETS

I nodes / 1* 13 /

P(I) destination or origin / 1* 13 /

VP(P) valid od pair with positive demand;

ALIAS (I,J,II,JJ),(P,Q);

…

NPOD(I,J,P)$(VP(P) AND ORD(I) EQ ORD(P) AND ORD(J) EQ ORD(Q) AND ORD(I) NE ORD(J))…

M(I,J,P) =E= SUM((I,J)$HARC(I,J), X(I,J,P)*(HW(I,J,“Cost”) + HW(I,J,“Lagm”)))

- SUM((I,J)$RARC(I,J), Y(I,J,P)*(RW(I,J,“Cost”) + RW(I,J,“Lagm”)) - C(I,J));

I got the error information in the line “SUM((I,J)$HARC(I,J)”, and it said set is already control. Would anyone kindly point out how can i figure this out? Thanks!

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