We derive the implication rule using the rules introduced last week.

We use the rules to reduce a sequent to a conjunction of simpler sequents. In this example we find that the expression asserted by the sequent is a tautology — it is equivalent to the empty…

We use the rules to reduce a sequent to a conjunction of simple sequents, sequents that only mentions propositional letters, with no connectives, and no repetitions — in this example, we find…

We interpret additional predicates before the turnstile. These simply express validity in a sub-universe. This means that for any sound rule the corresponding rule with additional predicates is…

The following videos introduce sequents, a far-reaching generalisation of the idea underlying Aristotle's propositions. We have already discussed the introduction of multiple antecedents…

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