2021-07-01: Aligning \qedhere after TikZ diagram rak
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Getting the QED tomb properly aligned with the bottom of a
diagram can be annoying. Especially when you have done it in the
past, but have forgotten how. To help future me out, the
solution is to wrap the diagram in a gathered environment with
bottom alignment, and then to add a magic new lign right after
you close the (in this case) tikzcd environment:
