Logic / Logic 126 · Atom · ~20 seconds

Translating "Only If"

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State

"p only if q" means p ⊃ q — the "only if" clause is the *consequent*.

Show

"You may board only if you hold a ticket" — Board ⊃ Ticket. Not the reverse: a ticket doesn't guarantee boarding.

Watch for

This is video 089's trap wearing propositional clothes. "Only" reverses expectations in both systems.