- alf: |-
    project(union(suppliers_in_london, suppliers_in_paris), [:name])
  optimized: |-
    union(project(suppliers_in_london, [:name]), project(suppliers_in_paris, [:name]))
- alf: |-
    allbut(union(suppliers_in_london, suppliers_in_paris), [:name])
  optimized: |-
    union(allbut(suppliers_in_london, [:name]), allbut(suppliers_in_paris, [:name]))