Remove common subexpressions here

[ltworf]

empty = πroom(σ id is None (people ⧓ person_room ⧓ rooms))

full = πroom(σ r==room and i != id ( πr,i (ρ room➡r, id➡i ( people ⧓ person_room ⧓ rooms )) * π room,id (people ⧓ person_room⧓rooms)))

πroom (rooms) - empty - full ⋈ person_room ⋈ people

The same joins are performed multiple times and will not be optimised, which was the entire point of the multiline optimizations.