Clarified docs for calc.perm,rem,quo (#2408)

crates/typst-library/src/compute/calc.rs

@@ -445,8 +445,12 @@ pub fn fact(
 
 /// Calculates a permutation.
 ///
+/// Returns the `k`-permutation of `n`, or the number of ways to choose `k`
+/// items from a set of `n` with regard to order.
+///
 /// ```example
-/// #calc.perm(10, 5)
+/// $ "perm"(n, k) &= n!/((n - k)!) \
+///   "perm"(5, 3) &= #calc.perm(5, 3) $
 /// ```
 #[func(title = "Permutation")]
 pub fn perm(
@@ -482,6 +486,9 @@ fn fact_impl(start: u64, end: u64) -> Option<i64> {
 
 /// Calculates a binomial coefficient.
 ///
+/// Returns the `k`-combination `n`, or the number of ways to choose `k`
+/// items from a set of `n` without regard to order.
+///
 /// ```example
 /// #calc.binom(10, 5)
 /// ```
@@ -779,6 +786,9 @@ pub fn odd(
 
 /// Calculates the remainder of two numbers.
 ///
+/// The value `calc.rem(x, y)` always has the same sign as `x`, and is smaller
+/// in magnitude than `y`.
+///
 /// ```example
 /// #calc.rem(20, 6) \
 /// #calc.rem(1.75, 0.5)
@@ -796,11 +806,12 @@ pub fn rem(
     Ok(dividend.apply2(divisor.v, Rem::rem, Rem::rem))
 }
 
-/// Calculates the quotient of two numbers.
+/// Calculates the quotient (floored division) of two numbers.
 ///
 /// ```example
-/// #calc.quo(14, 5) \
+/// $ "quo"(a, b) &= floor(a/b) \
-/// #calc.quo(3.46, 0.5)
+///   "quo"(14, 5) &= #calc.quo(14, 5) \
+///   "quo"(3.46, 0.5) &= #calc.quo(3.46, 0.5) $
 /// ```
 #[func(title = "Quotient")]
 pub fn quo(