Restriction formal expression

Symbol-free definition
A restriction formal expression is the expression of a subgroup property using a restriction formalism. A typical restriction formal expression looks like:

$$a \to b$$

meaning that every element satisfying property $$a$$ in the set corresponding to $$G$$ is related to an element satisfying property $$b$$ in the set corresponding to $$H$$. (this definition is for the existential restriction formalism. Analogous definitions exist for other formalisms.