def _is_bn_diff_doctypes(dyad):
    """Check if a dyad is between two different doctypes.

    Args:
        dyad (tuple): two-item tuple where each item is a dict which represents a document

    Returns:
        ind (bool): True if the dyad is between two different doctypes

    """
    if dyad[0]["doctype"] != dyad[1]["doctype"]:
        ind = True
    else:
        ind = False
    return ind