Between the two authors here (McKinsey and Tarski), they cite each other 7 times, with 14 citations, giving 50% outgoing self-citation, however this paper also

Between the two authors here (McKinsey and Tarski), they cite each other 7 times, with 14 citations, giving 50% outgoing self-citation, however this paper also received incoming citations contemporaneously... https://doi.org/10.2307/2268135 https://doi.org/10.2307/2268135