Definition:Marked Leaf

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Definition

Let $T$ be a semantic tableau.

Let $t$ be a leaf of $T$.


Then $t$ is marked iff it has occurred in Step 3 of the Semantic Tableau Algorithm.

Otherwise, it is called unmarked.


Marked Closed Leaf

A marked leaf $t$ of $T$ is marked closed iff its label $U \left({t}\right)$ contains a complementary pair.

This can be designated by adding to $t$ a second label $\times$.


Marked Open Leaf

A marked leaf $t$ of $T$ is marked open iff its label $U \left({t}\right)$ does not contain a complementary pair.

This can be designated by adding to $t$ a second label $\odot$.


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