Turnstile Figures of Opposition

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This paper has been presented at
The 6th World Congress on the Square of Opposition
November 1-5, 2018, Orthodox Academy of Crete
it is inlcuded in the corrsepodning volume: J.-Y.Beziau and I.Vandoulakis (Eds.)
The Exoteric Square of Opposition, Birkhäuser, Basel, 2021.