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Theorion

Touying can work properly with the Theorion package, you can directly use the theorion package. Additionally, you can use #set heading(numbering: "1.1") to set numbering for sections and subsections.

Note: To make animation commands like #pause work properly with theorion, you need to use config-common(frozen-counters: (theorem-counter,)) to bind counters that need to be frozen.

#import "@preview/touying:0.6.3": *
#import themes.university: *
#import "@preview/numbly:0.1.0": numbly
#import "@preview/theorion:0.4.1": *
#import cosmos.clouds: *
#show: show-theorion

#show: university-theme.with(
  aspect-ratio: "16-9",
  config-common(frozen-counters: (theorem-counter,)),  // freeze theorem counter for animation
)

#set heading(numbering: numbly("{1}.", default: "1.1"))

= Theorems

== Prime numbers

#definition[
  A natural number is called a #highlight[_prime number_] if it is greater
  than 1 and cannot be written as the product of two smaller natural numbers.
]
#example[
  The numbers $2$, $3$, and $17$ are prime.
  @cor_largest_prime shows that this list is not exhaustive!
]

#pause

#theorem(title: "Euclid")[
  There are infinitely many primes.
]

#pagebreak(weak: true)

#proof[
  Suppose to the contrary that $p_1, p_2, dots, p_n$ is a finite enumeration
  of all primes. Set $P = p_1 p_2 dots p_n$. Since $P + 1$ is not in our list,
  it cannot be prime. Thus, some prime factor $p_j$ divides $P + 1$. Since
  $p_j$ also divides $P$, it must divide the difference $(P + 1) - P = 1$, a
  contradiction.
]

#corollary[
  There is no largest prime number.
] <cor_largest_prime>
#corollary[
  There are infinitely many composite numbers.
]

#theorem[
  There are arbitrarily long stretches of composite numbers.
]

#proof[
  For any $n > 2$, consider $
    n! + 2, quad n! + 3, quad ..., quad n! + n
  $
]
Touying example output

Why frozen-counters is Required​

Touying renders each subslide by re-evaluating slide content. Without frozen-counters, Theorion's internal theorem-counter would increment on every subslide, causing theorem numbers to jump unexpectedly.

config-common(frozen-counters: (theorem-counter,)) tells Touying to capture the counter value at the start of each slide and restore it before rendering each subslide, so theorem numbers remain consistent across animation steps.

Multiple Counter Types​

If you also have figure counters that should be frozen:

config-common(frozen-counters: (theorem-counter, figure.where(kind: image)))

Cosmos Styles​

Theorion ships with several visual styles. The example above uses cosmos.clouds. Others include cosmos.fancy, cosmos.aurora, and more. See the Theorion documentation for details.