def val2str(val):
    """Convert VAL (number) into a string

    This function works like "str", but it substitutes any trailing
    hyphen sign with a Unicode minus sign, which is typographically
    more correct.
    """
    s = str(val)
    if s[0] == "-":
        # Use the Unicode minus sign
        s = "−" + s[1:]

    return s