Single or double dash between coauthors names?

Should I type:

In the foundational paper of Eells-Sampson (...)

or

In the foundational paper of Eells--Sampson (...)

So, single or double dash in the tex code between "Eells" and "Sampson" (the two co-authors)?

Sorry if the answer is somewhere on this site, I couldn’t find it.

EDIT: According to Mico in the comments, I should not write either. How about when writing the "theorem of Eells-Sampson" or the "Euler-Lagrange equations"? Sorry if you find, like Mico, that this is a completely different question that has absolutely nothing to do with my original question.