def subtract(x, subset):
    """Remove elements of subset if corresponding label ID sequence already exist in x.
    
    Args:
        x: Set of hypotheses.
        subset: Subset of x.
        
    Returns:
       final: New set of hypotheses.
    """
    final = []

    for x_ in x:
        if any(x_.yseq == sub.yseq for sub in subset):
            continue
        final.append(x_)

    return final