This paper talks about "$M^\natural$-concave functions". The paper defines what an M$^\natural$-concave function is, but, I would like to know specifically what does the $\natural$ symbol mean? Why is it called "natural" and where else in mathematics is it used?

  • 1
    $\begingroup$ See Natural sign (in music). $\endgroup$ Sep 29, 2016 at 5:55
  • $\begingroup$ This post on TeX.SE implies that the OP was wishing to use it as a boundary connected sum in analogy to how $\sum$ is used for ordinary summation. Looking at other texts about boundary connected sums however, I see $\#$ or some other variation being used instead. $\endgroup$
    – JMoravitz
    Sep 29, 2016 at 6:33
  • $\begingroup$ Should we read for example M natural? $\endgroup$
    – haleh
    May 27, 2017 at 8:30
  • $\begingroup$ It's the natural sign from music, to undo a sharp or flat set by the key signature. Unsure how it's used in math. Here's the Unicode for the symbol: fileformat.info/info/unicode/char/266e/index.htm $\endgroup$
    – 2540625
    Jul 4, 2019 at 3:44


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