Maybe there is no universally agreed definition of 'fact' because it is used with different meanings such as these:

1) Mathematically proven truth in a given axiom system (typically relying on 2-value-logic).

2) A theory agreeing to all data known or observed thus far. [Physics relies on these kinds of theories. New experimental evidence can turn a previously believed theory into a falsehood or approximation. For Go, where (1) is not available yet, (2) is a weaker but otherwise possibly strongest description for a theory meeting the entirety of all known played Go games and constructed examples.]

3) Something informally generally believed to be true but lacking (1) and (2).

4) Like (3) without "generally", but only majority opinion or a predominating opinion or a serious alternative opinion is available. [Courts might need to rely on such kinds of relatively weak decisions when evaluating alleged facts.]

Is that a fact?

For clarification, I have meant "for those Go-aspects for that (1) is not available yet". There are different facts of types (1), (2), (3) or (4) for different aspects of Go.

EDIT:

Cambridge International Dictionary of English:
"fact --- something which is known to have happened or to exist, esp. something for which proof exists, or about which there is information"

Globalwörterbuch / Teil 2 / Deutsch / English:
"sachlich --- 1. (faktisch) Irrtum, Angaben factual [...] (sachbezogen) Frage, Wissen relevant. 2. (objektiv) Kritik, Bemerkung objective [...]"

The Chambers Dictionary:
"factual --- pertaining to facts, actual"

It's cool to achieve (1) and (2) if you can, but at best, this accomplishment does not speak of an absolute "truth". It simply ascertains the logical consistency of the axioms in the system and/or the data that has been observed.

In the real world, the fundamental axioms that people choose to select can vary from person to person. People also have different experiences, which lends to different "datasets" from which they analyze and make decisions.

If all humans shared a common set of input data and axioms, perhaps we can state that X is a more factual argument than Y.

But since this is not the case, at some point, all arguments have to come down to the fundamental axioms that preside in the system from which you are making decisions and/or the data that has been observed.

For this reason, I feel that "factual discussion" is not universally achievable, and will always be subject to the person interpreting the discussion as it has been presented to them.

Because of this, emotional arguments, arguments that do not appear to be formulated in the same methodology as standard research of modern times, and the like, cannot be universally said to be "less valid" than their "more scientific sounding" counterparts.

Admittedly, in this day in age, an approach that appears more objective and scientific is likely to be more widely accepted as "truth" among the academic community.

But I do not believe that this implies that such approaches are inherently more valid than other approaches. An argument can sound stupid, appear to be unfounded by data to the casual observer, and still be correct.

As human beings with a finite set of knowledge, however, it is not possible to make this distinction.

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be immersed

Factual discussion (in the sense of sachliche Diskussion) can include also criticism, refutation or counter-evidence if they provide alternative or possibly better reasoning. In contrast, emotional discussion "I want to (dis)believe this regardless of whether it relies on facts or reasoning" would not be factual discussion.

You question the power of truth within an axiom system. Although there can be systems of badly chosen axioms, mathematics and natural sciences have been very successful by relying on well chosen axioms.

For the sake of understanding many facts, it is unnecessary for all humans to use the same input data and axioms. For quite a few facts, all people can come to the same conclusions. E.g., a naive person can, by universal experience, conclude that each human being jumping up falls down back on earth and does not escape into the sky. A physician can conclude the same in terms of the timespace created by the earth's mass in comparison to a person's mass and initial velocity relative to the earth's surface.

Also in Go, it is possible to establish truths. E.g., a string with exactly 1 liberty can be removed by the opponent if it is the opponent's turn (in particular, the game has not ended yet) and the ko rules allow creation of the subsequent position. A mathematician can prove this for an arbitrary string; an informally thinking player can come to the same conclusion due to universal experience. A careless informally thinking person might overlook the conditions "opponent's turn" and "the ko rules allow creation of the subsequent position", but discussion can convince him that they can be relevant.

This comes down to degree of certainty, does it not? Some conclusions have a lot of data pointing to their likely validity. Many of the items discussed on the forum are more controversial. When enough data has been obtained such that these things become clear, I think it can then be argued that the "emotional type" arguments are not superior.

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be immersed

I guess that a lot of things discussed on L19 are not established facts indeed. This is different for research results. (Note: possible 'disbelief in research results due to insufficient study of what they are' is different from 'the research results themselves'. E.g., a few people might disbelieve "At the game end, bent-4-in-the-corner can sometimes live." because they neglected reading research results showing such examples, and still take the outdated rules maxim "Bent-4-in-the-corner is always dead." for granted.)