pub fn main(world: World) -> Void raises {
    var uppered: [4]u8 = [0_u8; 4]
    var lowered: [4]u8 = [0_u8; 4]
    let upper_text: Maybe<Span<u8>> = std.str.toUpperAscii(uppered, "Zero")
    let lower_text: Maybe<Span<u8>> = std.str.toLowerAscii(lowered, "Zero")
    if upper_text.has && lower_text.has && std.mem.eql(upper_text.value, "ZERO") && std.mem.eql(lower_text.value, "zero") {
        check world.out.write("string case ok\n")
    }
}