#let ru_alph(pattern: "а)") = {
    let alphabet = "абвгдежзиклмнопрстуфхцчшщэюя".split("")
    let f(i) = {
        let letter = alphabet.at(i)
        let str = ""
        for char in pattern {
            if char == "а" {
                str += letter
            }
            else if char == "А" {
                str += upper(letter)
            }
            else {
                str += char
            }
        }
        str
    }
    f
}

#let numbered_eq(content) = math.equation(block: true, numbering: "(1)", content)