UNI_BRIDGE · Proof & logic · PROOF.LOGIC.INTRO

Logic and quantifiers

Intuition

Understand first, compress later.

A proof is an unbroken chain of reasoning from definitions, assumptions and established results.

Switch representations

Truth tableP ⇒ Q

T — trueF — falserow where the compound is true

An implication is false only when the hypothesis holds but the conclusion fails. If P is false the statement claims nothing about Q, so it counts as true (vacuously). P ⇒ Q is true in 3 of the 4 cases; the gold marks in the margin flag exactly those rows.

Formal view

You can logic and quantifiers when you can recognise the underlying objects, select valid rules and check each step for equivalence or logical implication.

Why does it work?

This skill sits on a prerequisite network. If a step is unstable, repair the missing prerequisite instead of merely doing more items of the same type.