Which quantifiers are represented by the first two symbols ($\iota$ and $\mathcal{A}$) in the set in which Q belongs. I could not find a reference on the Quantifier Wikipedia article.
(Source: Introductory slide on Lambda Calculus (slide 32) in a slide-deck on grammars for parsing natural language sentences.)
Here's an example where the first one is used; might be helpful to pin-point which quantifier it represents in case the author used non-standard symbols.
(Source: Slide 45 in the same slide-deck.)
The iota ($\iota$) and script A ($\mathcal{A}$) are determiners, not quantifiers in the usual sense; they’re described later, in the slides titled Definite Determiners and Indefinite Determiners. The expression $\iota x.F(x)$ is a term representing the unique entity $x$ such that $F(x)$ is true when such an entity exists and is undefined otherwise; see also this web page. $\mathcal{A}$ is the indefinite counterpart of $\iota$: $\mathcal{A}x.F(x)$ selects any entity $x$ such that $F(x)$ is true. Thus, $\iota$ functions somewhat like the definite article the, while $\mathscr{A}$ functions rather like the indefinite article a(n). The examples in the relevant slides are fairly clear.