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That's all pretty embarassing, and related to Diptera philogeny. Separate R2 to R4 are present in e.g. Psychodidae (R1 is your Sc, by the way), in most of other families the branches of the radial sector are reduced to some extent, which gives us R2+3 and R4+5. The same applies to othe sectors (M, Cu, A). You still need an expert who will put it clear and simple for you (at least in case of Platypezidae).