def attributes_pairs(attributes, prefix='', medfix=' - ', suffix=''):
    """
    Make a list of unique pairs of attributes.
    Convenient to make the names of elements of the mixing matrix 
    that is flattened.
    """
    N = len(attributes)
    col = []
    for i in range(N):
        for j in range(i+1):
            col.append(prefix + attributes[i] + medfix + attributes[j] + suffix)
    return col