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List all the capital ships (bc) listed in the database.
C = π class (σ type = 'bc' Classes)
C ⨝ Ships
Find those countries that had both battleships and battlecruisers.
BB = π country (σ type = 'bb' Classes)
BC = π country (σ type = 'bc' Classes)
BB ∩ BC
Find those ships that where damaged in one battle, but later fought in another.
-- No esta del todo bien, algunos edge cases no los contempla (el barco se dañe en dos batallas consecutivas)
D = ρ D (π ship, battle (σ result = 'damaged' Outcomes))
BDATES = ρ BDATES (π date (σ D.battle = Battles.name (D ⨯ Battles)))
PB = π name (σ Battles.date > BDATES.date (BDATES ⨯ Battles))
VALIDBATTLES = σ Outcomes.battle = Battles.name (Outcomes ⨯ PB)
π D.ship (σ D.ship = Outcomes.ship ∧ result ≠ 'damaged' (D ⨯ VALIDBATTLES))
World Cup 2010
Liste los países con los que jugó la Selección Argentina.
good