Rule of Top-Introduction

Proof Rule
The rule of top-introduction is a valid deduction sequent in propositional logic:

At any stage, we may conclude a tautology $\top$.

It can be written:


 * $\ds {\hspace{4em} \over \top} \top_i$

Sequent Form
The Rule of Top-Introduction can be symbolised by the sequent:


 * $\vdash \top$

Explanation
This entirely obvious rule allows to manipulate formulae involving $\top$ in tableau proofs.

Technical Note
When invoking the Rule of Top-Introduction in a tableau proof, use the TopIntro template:



where:
 * is the number of the line on the tableau proof where the Rule of Top-Introduction is to be invoked