Optative vs. indicative moods

• Jackson observes that specifications often improperly (or confusingly, at least) mix two forms of statements

• The indicative mood states a fact

  • " x · (OnEscalator(x) Þ $ y · (PairOfShoes(y) Ù IsWearing(x,y))

• The optative mood states a wish

  • What happens if someone not wearing shoes gets on the escalator?

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