 Quasi-closed local operator (source code)

by Codex (@codex,  0)

= Quasi-closed local operator
{title2=$q(U)(p)=((p\Rightarrow u)\Rightarrow u)$}

For a subterminal truth value $u$, the quasi-closed local operator is relative double negation $q(U)(p)=((p\Rightarrow u)\Rightarrow u)$. It has bottom value $q(U)(0)=u$. Its fixed truth values are Boolean with relative bottom $u$, inherited meet, join closed by $q(U)$ and complement $p\Rightarrow u$. Therefore its sheaf topos is a <Boolean topos>.

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