The phrase "a mere fact" is correct and usable in written English.
It can be used to emphasize the simplicity or straightforwardness of a fact, often in contrast to more complex interpretations or opinions.
Example: "While many may debate the implications of the study, it remains a mere fact that the results were statistically significant."
Alternatives: "just a fact" or "simply a fact".
That the answer is East Germany is more than a mere fact.
That the systems these scientists create are usually pale shadows of human competence is a mere fact of robotics Today's must-read.
Yet Ransome had always seen his career as a mere fact gatherer as a detour, albeit a spectacular one in which he had witnessed the Bolsheviks' seizure of power at first hand and known Lenin and Trotsky (whose former secretary he married) personally.
His first revelation of his lover's death is delivered as a mere fact dropped into a sentence, and not dwelled on.
Species and subspecies are taxonomic levels generally considered as objective descriptors of biological reality, a mere fact at the origin of the numerous different studies proposed to date.
On the one hand, a mere fact that a stool donor has been living in a village for life doesn't make his or her microbiota a beneficial transplant.
As a result, the mere fact that he has chosen to represent a particular client, not to mention his fame and reputation gained from the Hussein trial, is sometimes enough to ensure an exoneration.
Of course, as with any such tool, even one as simple as a pencil, the mere fact that anyone can use it does not a genius make.
When inspired, the group catcalled in the direction of traffic — provoked by an angry driver, a hand gesture or a shout, the look of fear or disgust on an elderly face, or the mere fact of a particularly ostentatious vehicle, like a Humvee or a Bentley.
Popularity itself, and its correlate, celebrity, became an intrinsic value the mere fact of widespread knowledge and familiarity became a reason to pay attention.
While I don't believe we will move from a totalitarian state to a democracy by the mere fact of his visit, some acts have a symbolic significance that transcends their purposes.
