This breaks that <config>-ThornGuide target with

! Undefined control sequence.
l.40349     \bracket
                    { \frac{^{(4)}R}{16\pi} - \frac{1}{2} g^{\mu\nu}
? 
! Emergency stop.

new macros must be defined inside of the magic comments ideally just below the comment % Add all definitions used in this documentation here which the documentation template contains.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2827/twopunctures_bbhsf-defines-new-macro