I got the answer on StackExchange and was actually just about to find the answer myself. What is missing in Maruyama’s thesis was an index of symbols, that would have been helpful at least to know what the name of the symbols was, and so where to look in a long book on universal algebra.

]]>In “Natural duality, Modality, and Coalgebras”, in his thesis Meaning and Duality - From Categorical Logic to Quantum Physics, and elsewhere Yoshihiro Maruyama talks about $\mathrm{ISP}$, $\mathrm{ISP}$(M), how it is composed of $\mathrm{I}$, $\mathrm{S}$ and $\mathrm{P}$, but I can’t figure out what these stand for.

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