Just encountered two questions,
Is there a common genesis for ADE classifications?
IMO, they are very-very similar, but this is not really a duplicate case, rather, they sort of complement each other. At the first sight, the first one is less detailed and, accordingly, has more answers, providing more general information. On the other hand, the second one, although having only one answer, which is moreover quite specialized (to physics), but, again imo, it is asked in a better, deeper way, complements very nicely the first one, and I certainly would not recommend to close it. At the same time, I feel it is somehow not right that they are separate and only seen in each other's "Related" columns (which contain lots of other stuff, some more, some less related).
To add to the confusion, there is still another question, Are Dynkin diagrams of some universal construction?, which, this time, I find, is certainly a duplicate in the sense that it is subsumed by the first two - more precisely, it should be merged with the first, I think. But then, maybe, with the second rather with the first??
Is there a common opinion on MO how to deal with such cases?
I found a similar question on meta, Merging old duplicates? but similarly to my very question, it addresses slightly different aspects of the thing I want to know. Moreover, it has not got any answers, so...