def invert(testset):

    base12 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]

    invset = [(testset[0])]
    for s in range(len(testset)-1):
        interval = testset[s] - testset[s+1]
        if s == 0:
            inv_val = (testset[s] + interval) % 12
        else:
            inv_val = (interval + inv_val) % 12
        if inv_val < 0:
            inv_abs = base12[inv_val]
        else:
            inv_abs = inv_val
        invset.append(inv_abs)
    return(invset)