logic.day

P ∧ Q

The Proposition

Every chain of reasoning begins with a simple assertion. A proposition is the seed from which forests of inference grow -- a statement that dares to be either true or false, never both, never neither.

∀x (P(x) → Q(x))

Universal Quantification

For all things that share a property, a truth unfolds. The universal quantifier sweeps across every instance, binding them together in a single, inescapable conclusion. What holds for one must hold for all.

P, P → Q ⊢ Q

Modus Ponens

The engine of deduction. If we know a thing is true, and we know that thing implies another, then the implied thing stands proven. From two seeds, a third certainty blooms -- inevitable as sunrise follows the turning of the earth.

P ∧ ¬P ⊢ ⊥

Reductio ad Absurdum

Assume the impossible. Follow it to its breaking point. When contradiction flowers, the original assumption withers -- and truth emerges from the compost of impossibility. The most elegant proof technique is the art of constructive destruction.

∴ TRUE

Truth Emerges

From a proposition, a world unfolds. Each assertion creates a branching path -- follow it faithfully and truth crystallizes at the terminal node, clear as morning dew on a blade of grass.

∴ Q(a) for any a

Instantiation

The universal becomes particular. From the vast sweep of "for all," we pluck a single instance -- and it carries the full weight of universal truth. The general principle breathes life into every specific case.

Q.E.D.

Proof Complete

The chain holds. Each link forged in logical fire, each step as certain as the last. The conclusion stands not because we wish it, but because the structure of truth demands it. Quod erat demonstrandum.

¬P ∨ ¬(¬P)

Clarity Through Negation

From the wreckage of contradiction, truth rises purified. What cannot coexist reveals what must stand alone. The beauty of reductio is that it finds light by first embracing darkness completely.

Synthesis

Premise and conclusion converge. The split dissolves. What was two becomes one understanding -- not through compromise, but through the crystalline force of valid inference. Logic is not a cage; it is the architecture of clarity itself.

P → Q, Q → R ⊢ P → R