# Projection syntax - relational algebra

I'm trying to understand this paper and in Figure 1 page 389 there's a projection in the form of $$\pi_{d.id : s.id}$$. What does the colon mean? Because usually projections are simply $$\pi_{name}(R)$$

• What does the paper say it means? Jan 1 at 18:30
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– D.W.
Jan 1 at 22:54

. . . Π d.id:s.id ((students s ⋈ s.id=e.sid exams e) ⧑