"A" as an indefinit article means in the following cases "each and every", right?
Abortion: In the U.S, "A" woman enjoys a constitutional right to have an abortion during the first trimester of "her" pregnancy. In this sentence, "A" means every/each woman enjoys a constitutional right to have an abortion during their first trimester of "her" pregnancy. Using "A" in this context emphasizes that there is no exception, right? In other words, and since this a rule and rules apply to all people equally, Using "A" was a smart or rather the right choice, right?
"A" square has four equal sides. Meaning, every/each square has four sides. "A" emphasizes that there is no exception, right? in other words, no way that a square will have 5 sides, right?
The bottom line is, "A" is better used in law and when we want to state a rule. Of course we can use Each and every. The thing is, may people who learn English as a second language, thinks that "A" is only an indefinite Article.