Function apply_adverb 

pub fn apply_adverb<'a>(
    expr: &'a LogicExpr<'a>,
    adverb: Symbol,
    interner: &mut Interner,
    expr_arena: &'a Arena<LogicExpr<'a>>,
    term_arena: &'a Arena<Term<'a>>,
) -> &'a LogicExpr<'a>

Adds an adverbial modifier to an event.

Transforms ∃e(P(e) ∧ ...) into ∃e(P(e) ∧ Adverb(e) ∧ ...).