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Hello Guenther,
Well, the genus Platycheirus doesn't have a yellow face with a black stripe in the middle like this one has. Together with the yellow banded abdomen this immediatly points out to a species of Parasyrphus. Finally, the antennae are black and it's third leg is almost entirely black, only the knee is a bit yellowish.
To me, all this points out to a female of Parasyrphus lineolus!
Greetings,