def is_nonnegative_integer(argument) ->bool:
    """
    Is true when ``argument`` equals a nonnegative integer.

    ..  container:: example

        >>> abjad.mathtools.is_nonnegative_integer(99)
        True

        >>> abjad.mathtools.is_nonnegative_integer(0)
        True

        >>> abjad.mathtools.is_nonnegative_integer(-1)
        False

    """
    if argument == int(argument):
        if 0 <= argument:
            return True
    return False
