为什么第一个就显示语法错误

model
sets:
factory/1..4/:c,x;
plant/1..3/:b;
cool(plant,factory):a;
endsets
data:
c=1,2,3,4;
a=1,-1,-1,1
1,-1,1,-3
1,-1,-2,3;
b=0,1,-0.5;
enddata
min=@sum(factory:c*x);
@for(factory(j):@sum(a(i,j)*x(j)=b(i));
@for(factory:@free(x));
end