fn leap(year: u32) -> Bool {
    if year % 400 == 0 {
        return true
    }
    if year % 100 == 0 {
        return false
    }
    return year % 4 == 0
}

pub fn main(world: World) -> Void raises {
    if leap(2000) && !leap(1900) {
        check world.out.write("leap year ok\n")
    }
}