Mathematician and European leader wanting introduction (5)

I believe the answer is:

euler

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'mathematician' is the definition.
(I've seen this before)

I don't understand how the rest of the clue works.

(Other definitions for euler that I've seen before include "Leonhard -----, founder of mathematical analysis" , "Leonhard -, C-eighteen Swiss mathematician" , "Leonhard --, C18 Swiss mathematician" , "calculating foreigner" , "Swiss scientist" .)

I've seen this clue in The Independent.

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