[tex-k] a technical error in MFbook

[胡亚捷 (Hu Yajie)]

Page C292, line -10
Change "known p-q" to "known (p-q)", because the syntax of Chapter 25
tells us that "known" applies to primary expressions and subtraction
occurs on the tertiary level of precedence.

p=q;
show if known p-q: p=q else: false fi;    % produces errors
show if known (p-q): p=q else: false fi;  % true

(It's near the deadline and I still haven't gone through the whole book...)

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Previous reports:
https://github.com/dine2014/texbook-mfbook-bugs/blob/master/bugs.md