"== This theorem should not be called Marden's theorem? == 

 In Dan Kalman's paper cited in the article, he writes:  

 ""I call it Marden's theorem because I read it in a book by Marden, although Marden himself credits Siebeck with the original discovery."" 

 The fact that Kalman writes that *he* calls it Marden's theorem strongly suggests there is no historical precedent for this name.  The further fact that Marden himself credits Siebeck is yet another reason to give credit where credit is due: to Siebeck. 

 This theorem should be called Siebeck's Theorem.  There are already enough misattributions in mathematics (e.g., the Cayley numbers were discovered by Graves).  There is no reason to knowingly perpetuate yet another one."