Is there an equivalent to Latex's \cancelto in Typst?

Questions
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Latex has “cancelto” in math mode. It’s similar to “cancel”, but it’s an arrow instead of a line, and it points to an additional parameter which is supposed to indicate what expression evaluates to. Most often, it’s 0 or 1 (see image). Ideally it would be implemented by the developers, but in the meantime, is there a way to reproduce this with a show rule or something? Thanks!

Iz5tK
Iz5tK901×241 38.1 KB

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I’m not aware of an easy solution for this, you might as well create a new issue for this.

Here is my very rough solution:

#let cancelto(body, to) = {
  let arrow = rotate(-55deg, scale(x: 170%, $-->$))
  context {
    let m = measure(body)
    let (w, h) = (m.width, m.height * 2)
    set place(center + horizon)
    // block(height: h * 2.5, align(horizon, body)) // Add vertical margins.
    body
    place(dx: -w * 0.5, dy: -h * 0.1, arrow)
    place(dx: w * 0.3, dy: -h * 1.1, $0$)
  }
}

$(diff T)/(diff t) = k (diff^2 T)/(diff z^2) + v_z (diff T)/(diff z)$

$cancelto((diff T)/(diff t), 0) = k (diff^2 T)/(diff z^2) + v_z (diff T)/(diff z)$

$(diff T)/(diff t) = k (diff^2 T)/(diff z^2) + v_z (diff T)/(diff z)$

image

image

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Awesome, thanks. I’ll try to find a way to determine the angle and scale automatically. And I’ll create the issue as well.

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4

Be sure to link it here (both ways is even better). :)

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A relevant issue would be this one probably Add arrow caps for stroke · Issue #1532 · typst/typst · GitHub.

Ideally, you would write

$
  cancel(a x + b, stroke: #(cap: "arrow"))
$

or another syntax that is less verbose and more discoverable.

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6

There’s another issue that was already created for this and was closed as not planned. The developers think it would be better as a package.

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I had a feeling that this is more of a package-level functionality. And since it’s a part of a package in LaTeX, this further proves the point. You can make a package yourself at any point if you want, otherwise we’ll have to wait for someone else to do it.

8

Here is the Rust code for the cancel() function, in case there’s something helpful there:

9

Now that Typst v0.12.0-rc1 is out, you can also use stretch for long arrow:

  // let arrow = math.stretch(sym.arrow.tr, size: 230%)
  let arrow = rotate(-55deg, math.stretch(sym.arrow.r, size: 230%))

I also realized that if you are OK with 45 degree arrows, you can remove the rotate() call and use a specific arrow glyph instead: https://typst.app/docs/reference/symbols/sym/?query=arrow.

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