Learn English – Meaning of “under study”

"Classical Mechanics is a well known field of Mathematics." Do you even listen to yourself...? – Najib Idrissi 19 hours ago

The user "Najib Idrissi" asks the author of the sentence Classical Mechanics is a well known field of Mathematics. to read that statement for themselves. Najib makes sure that the author will realize the scientific mistake in that sentence and, in short, "will come to their senses."

It's like your friend has told you something very oddly wrong, and you didn't expect him to say so. You tell him/her to listen to himself/herself, so that s/he will realize the mistake they've made. In this case, it seems very rudimentary to the mathematicians that "classical mechanics" are a physics' subject, and hardly related to math. So, "well known", as it means that "many are familiar with it being a part of mathematics" seems a very idiotic expression to them, as if the author didn't know what they were typing, or simply, talking about.

If you ask me, there is a bit of negative connotation in this sentence, but it wouldn't be considered as offensive. (As "offensive" is too strong for it)

In fact, the expression "listen to yourself" is commonly used in the area of philosophy when there's a speak of art of communicating between humans.

philosophy reference 1

philosophy reference 2

The third

And this is a nice example of a similar usage. (Though it contains the expression and not the exact question)

in Google books

The laws of each jurisdiction are different, so without researching I could not say for sure. If this is an important question for you, you must ask someone who works in the Irish government to be specific.

There is also a question of what it means to be "resident". This can be very complicated but usually requires you to live in that place for a significant portion of the year, obtain local documentation (get a license, pay taxes, etc), or own property (and live in it). I don't know what those laws are for Ireland, so you will have to research that as well.

Without further explanation I would assume that it means, going back five calendar years (not including the current year), you had to have been resident for at least three out of those five calendar years. It may include the current year if it is late enough in the year that you can establish "residency" for this year.

Again, this is just a casual reading, and should not be taken as actual advice. Please do the research and ask.