The propositional skeleton $\skel$ of a formula $\varphi$ is obtained by replacing each occurance of a $\Theory$-literal with a propositional variable.

An example for a formula $\varphi$ in $\LIA$:

$$ \varphi \coloneqq (x > y) \lor (x > z),$$
and the corresponding skeleton $\skel$:

$$ e_1 \lor e_2, $$
where $e_1 \equiv x > y$ and $e_2 \equiv x > z$.