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Bertrand,

This looks to me like a member of Trichomyia; this genus has appeared in the ID queries forum before (though I misremember where). While the most widely distributed European species is Trichomyia urbica Haliday, there is no guarantee you've seen that species. Please note: the Fauna Europaea database is missing three or four of the species now known from their area of coverage (all of the omissions are local species not presently recorded from France).

Arthur