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This category contains results about tautology in the context of propositional logic.

A tautology is a statement which is always true, independently of any relevant circumstances that could theoretically influence its truth value.

It is epitomised by the statement form:

$p \implies p$

that is:

if $p$ is true then $p$ is true.

An example of a "relevant circumstance" here is the truth value of $p$.

The archetypal tautology is symbolised by $\top$, and referred to as Top.