Rabbi, do you yourself observe the second festival day? And if so, what do you think would be needed in order to abolish it (a Sanhedrin)?

You are mistaken.
The Rif explicitly rules that in the Land of Israel one needs two days.
The Baal HaMaor there cites Rabbenu Ephraim, a student of the Rif, that the Land of Israel reverted to being like the seat of the court, and one day is required. There in Baal HaMaor it is also explained that the custom in the Land of Israel until the arrival of the sages of Provence was one day. Nachmanides writes in Milchamot there that this is the custom of the ignoramuses and should not be taken into account.
Everything depends on the Talmudic passage about nullifying the ordinance not to accept the witnesses from minchah and onward, by Rabban Yohanan ben Zakkai.

What I wonder is: how do you have the nerve to express opinions when you do not even possess the initial basic knowledge of the topic?

I did not write my question as an “ad hominem” but only about the matter itself. In my humble opinion, it is proper to leave the discussion that way. Besides, every person is entitled to hold his own opinion, even if the answer does not find favor in your eyes.

Mordechai, there are people who enjoy lashing out. That’s perfectly fine. Just ignore it.
Indeed, this is not the Rif’s view but that of his student Rabbenu Ephraim. Other than that, everything I said stands.

At the end of the day, you expressed a firm opinion on a topic whose basics you did not know.
I wonder whether it is serious to conduct yourself this way.
What does that have to do with “ad hominem”? Just as in a medical matter, a person who is not familiar with the details would not express an opinion if he is a serious person, the same applies in matters of Jewish law.
It is not dishonorable to say, “I don’t know.” Rashi also did this from time to time.
There is a Talmudic topic of one who errs in an explicit Mishnah and one who errs in judgment. Here, sir, you erred in an explicit Mishnah, and setting the record straight is not lashing out.

Mordechai raised the “ad hominem” point, not me.
Your previous message (as well as this current one) was pure lashing out. That is because there was not one relevant detail in it that I had not taken into account. There was a mix-up between the Rif and his student, that’s all. Why does that matter at all to the substance of the issue? To compare this to giving a medical opinion without medical knowledge, or to someone who errs in an explicit Mishnah, raises serious questions about your understanding of logic and your reading comprehension. Therefore I judged you favorably and wrote that you intended to lash out. If the truth is that you did not intend that, the alternative is much less flattering to you.

Again, as is your habit, you find it difficult to admit your failures, and you try to mock whoever points out your mistakes.
To express firm positions without being versed in the topic is a mixture of arrogance and irresponsibility.

Hello David.

Although Rabbi Michael Abraham suggested ignoring your remarks, I nevertheless wish to address them because you responded to a question that I directed to the Rabbi. In effect, you used my words to attack the Rabbi.

So know this:

When one uses inappropriate expressions and harsh words, then even if within those inappropriate remarks there may perhaps be sensible points, they are not heard.

That is a rule!
With blessings, and happy holiday.