Barwise and Moss's book Vicious Circles presents the anti-foundation axiom using the notion of solutions to certain systems of equations in set theory called flat systems. Their Theorem 7.1 states that the solutions sets to two flat systems are equal iff the two systems are bisimilar. I would like to see the original source for this, but unfortunately, the historical remarks at the end of the chapter just say it's "due to (1988)". Presumably, the author's name has gone missing from this reference. Can anyone point me at a reference, please. Or explain if I have misunderstood Barwise and Moss's way of giving the reference.
Bisimulation in the solution-set formulation of the anti-foundation axiom.
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