It was my understanding that questions concerning formal logic (classical, propositional, predicate, etc.) were welcome in the Philosophy SE. Counter to my intuition, this question regarding how to formulate an inference rule from in tautological form was put on-hold as "off-topic", with the official reason "the question itself doesn't seem to be about philosophy, and is therefore not a good fit for our site."
Are technical questions in logic not welcome here? Sometimes I post questions in mathematical logic over at the Math SE, but I honestly appreciate the more philosophical perspective of the philosophers and logicians here, something I take into consideration when deciding whether to post at Math SE or Philosophy SE. It's not clear to me which questions are only welcome at Math SE and not here. The notion of where logic ends and mathematics begins is undecided in the academic community. For instance, does propositional logic belong to Philosophy, and predicate logic belong to Mathematics? What about sequent calculus? I suspect any hard line one attempts to draw would be disputed by those on both sides. I, personally, would have a hard time delimiting the boundaries of each discipline.
The impression I gathered from this post, however, is that technical questions are welcome in both philosophy and mathematics SE:
In the end, I believe that many logic questions could be asked either here or on the mathematics sites. If you ask a logic question here, it seems that you are more likely to get an answer with a greater level of philosophical gloss, with philosophically oriented examples, for example; and if you ask on the math site you will get an answer with greater level of mathematical gloss and mathematical examples. So my advice is to ask in the forum that appeals to you. But don't shy away from asking technical logic questions here, since there are people here who are interested and can answer.
Answers to the question Is "Stack exchange is not the place to learn first order logic" a correct statement? seemed to echo similar sentiments: that SE is a platform for "learning together" and specific questions about first-order logic are "absolutely on-topic".
Does Philosophy SE have an official policy on which questions in logic are excluded to Math SE? How is it decided which questions are too technical (or insufficiently "philosophical") to be deemed on-topic at Philosophy SE?