הֲלוֹא halo' from ה ha (interrogative prefix) and לוֹא lo' (negative) forms a negative question, often a "rhetorical question". Two examples in Amos:

6:13 where the phrase introduced by halo' becomes an assertion, even a boast and

9:7 where the negative effect is marked, "are you not like..." = "are you any different from..."