There are four ways of writing the name of the mathematician
and the things named after him: Mobius, Moebius, Möbius, and Möbius.
Unfortunately the E2 search and hardlink mechanism does not recognize o and ö as the same letter, and of course oe will not match either. And HTML entities like ö should never be used in node titles. So I have decided the best compromise is to use plain O, and move all relevant write-ups across to the plain-O title.
If in due course the search mechanism is improved, it will be possible to give Herr Möbius and all his works the umlaut they deserve.
Of course this does not apply to nodes in which some other spelling is part of a different proper name, as in the graphic artist noded above.