In the first formula, after 1/9 , isn't better to write "- ..." instead of "+ ..."? I understand that, by writing "+ ...", the author may be denoting "+ -1/11", that is, "plus whatever comes next"; if that's the case, OK.

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## Plus sign or minus sign?

In the first formula, after 1/9 , isn't better to write "- ..." instead of "+ ..."? I understand that, by writing "+ ...", the author may be denoting "+ -1/11", that is, "plus whatever comes next"; if that's the case, OK.