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Thank you, Sundew, for the good news and the first-class pictures. I'm also grateful to you for guiding me to the extremely useful internet key which is the sort of detailed key I had been looking for, but couldn't find. The wing pattern in the drawing also corresponds exactly with the one in the photos (particularly your second and my first picture). Carlo Monari, by the way, in his comment referred to Pjotr who is obviously one of the co-authors of your illustrated guide and also - I now realize - author of the excellent book The European Families of the Diptera which I recently bought. The diptera world, it seems, is a small world.
Kind regards,
Hans Theo K.