Minor fix

Author: JulStraus

src/model.jl

@@ -282,7 +282,7 @@ function variables_flow(m, ℒ::Vector{<:Link}, 𝒳ᵛᵉᶜ, 𝒫, 𝒯, model
     end
 
     # Create new flow variables for specific resource types
-    for p_sub in res_types_vec(𝒫)
+    for p_sub ∈ res_types_vec(𝒫)
         variables_flow_resource(m, ℒ, p_sub, 𝒯, modeltype)
     end
 end