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In extended relational algebra (aggregation being allowed) do you have to project all attributes that you use in a statement? So for example in the query below the attributes A.FO_ID and A.Arrival are not in the projection. Is this valid?

π A.Arrival_Airport, A.Arrival_Airport_Name ρ A (OF_OFFER) ⨝ A.FO_ID =   
Find_Max.FO_ID and A.Arrival = Find_Max.Max_Arrival_Time ρ 
Find_Max (π B.FO_ID, Max_Arrival_Time γ B.FO_ID; MAX(B.Arrival) → 
Max_Arrival_Time ρ B (OF_OFFER))

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