Hello, I’m taking my first steps into Julia and I’m trying to modelate a LP. I wrote the following constraint:

```
@constraint(m, ctte_equilibre[r in set_regions, tec in tech_by_site[r], dy in div_years, y in years, t in timeslice],
demand_df[Symbol(r)][tl] for tl in 1:size(periode_demande,1)==sum(x_prod[r, tec, dy, y, t]))
```

That gives me the following error:

```
LoadError: In @constraint(m,ctte_equilibre[r in set_regions, tec in tech_by_site[r], dy in div_years, y in years, t in timesli
ce],(sum(x_prod[r, tec, dy, y, t]) == (demand_df[Symbol(r)])[tl] for tl = periode_demande)): Constraints must be in one of the follow
ing forms:
expr1 <= expr2
expr1 >= expr2
expr1 == expr2
lb <= expr <= ub
```

The constraint related to demande_df can be expressed in a traditional loop as follow and I can acess all the elements desired at a time.

```
for r in set_regions
for tl in 1:size(periode_demande,1)
print(demand_df[Symbol(r)][tl], '\n')
end
end
```

However, when I wrote in the reduced to way in order to be able to pass it as a constraint, it seems don’t be appropried because it returns a object called "Generator{Base.Iterators.Prod2{Array{Int64,1},Array{String,1}},##481#482} "

that I know nothing about. See bellow the reduced way I used:

```
demand_df[Symbol(r)][tl] for tl in 1:size(periode_demande,1),r in set_regions)
```

When I use this reduced way I cannot anymore to see any element at a time.

Anyone could help me to understand my problem ? Thanks in advance.