נתונה הפעולה mystery המקבלת שתי מחרוזות:

def mystery(s1, s2):
    out1 = ""
    out2 = ""
    for i in range(len(s1)):
        ch = s1[i]
        pos = s2.find(ch)
        if pos == -1:
            if out1.find(ch) == -1:
                out1 = out1 + ch
        else:
            if out2.find(ch) == -1:
                out2 = out2 + ch
    return out1 + out2