How can I right align the QED symbol after a proof?

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4

One unfortunate edge case with this solution is if the QED symbol doesn’t fit into the last line. Then, the h(1fr) remains in the second-to-last line and the QED symbol is on the left side of the last line.

A possible fix is adding a Unicode Word Joiner (sym.wj) after the spacing.

#let proof(body) = block(width: 100%, fill: rgb("#EEEEEE"), {
  [_Proof._ ]
  body
  h(1fr)
  sym.wj
  sym.space.nobreak
  $qed$
})

However, this also forces the last preceding word to the next line. If this is not desirable, one could add a zero-width box before the spacing (which will then be forced to the next line instead of the last word, to no visible effect).

#let proof(body) = block(width: 100%, fill: rgb("#EEEEEE"), {
  [_Proof._ ]
  body
  box(width: 0pt)
  h(1fr)
  sym.wj
  sym.space.nobreak
  $qed$
})

This is obviously somewhat obscure and requires intricate knowledge of Unicode and Typst’s paragraph layout. I also only came up with this solution now even though I’ve thought about this problem a few times before. I’m not 100% sure whether there are cases where it doesn’t work correctly, but it any case it felt worth sharing.

Edit: Added nobreak spaces to ensure that there is a minimum amount of space before the proof square.

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