import itertools
def inclusion_and_exclusion_theorem(n):
    xs = []
    for i in range(0, n):
        xs.append(chr(ord('A') + i))
    ys = []
    for i in range(1, n + 1):
        items = itertools.combinations(xs, i)
        items = list(list(x) for x in items)
        ys.append(items)
    sign = True
    s = ""
    for i0 in ys:
        m = []
        sign = not sign
        for i1 in i0:
            m.append("n(" + "∩".join(i1) + ")")
        if sign:
            s += " - " + " - ".join(m)
        else:
            s += " + " + " + ".join(m)
    if s[0:3] == ' + ':
        s = s[3:]
    return s;
print(inclusion_and_exclusion_theorem(3))
 

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