# Definition:Marked Leaf

(Redirected from Definition:Unmarked Leaf)

## 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 $\odot$.