def check_for_workshop_prefix(seq):
    """
    Returns either original sequence and empty list or trims "W"
    from the front of the sequence.
    """
    if len(seq) <= 2:
        return seq, []

    # workshop alleles start with W
    if seq[0].lower() == "w" and seq[1].isdigit() and seq[2].isdigit():
        return seq[1:], ["W"]
    else:
        return seq, []