\set ECHO none
city|classification|n|formula
Berlin||2 (*)|δ(Ellen ⊕ Susan)
New York||2 (*)|δ(John ⊕ Paul)
Paris||3 (*)|δ(Dave ⊕ Magdalen ⊕ Nancy)
|unclassified|1 (*)|δ(John)
|restricted|2 (*)|δ(Paul ⊕ Nancy)
|confidential|1 (*)|δ(Dave)
|secret|2 (*)|δ(Ellen ⊕ Susan)
|top_secret|1 (*)|δ(Magdalen)
||7 (*)|δ(John ⊕ Paul ⊕ Dave ⊕ Ellen ⊕ Magdalen ⊕ Nancy ⊕ Susan)
(9 rows)