# A simple theorem not noticed before

Today I have noticed a new simple to prove theorem which is missing in my article:

Theorem If $( \mathfrak{A}; \mathfrak{Z})$ is a join-closed filtrator and both $\mathfrak{A}$ and $\mathfrak{Z}$ are complete lattices, then for every $S \in \mathscr{P} \mathfrak{A}$

$\mathrm{Cor}' \bigsqcap^{\mathfrak{A}} S = \bigsqcap^{\mathfrak{Z}} \langle \mathrm{Cor}' \rangle S.$

Particularly if $S \in \mathscr{P} \mathfrak{Z}$, this theorem reduced to the formula:

$\mathrm{Cor}' \bigsqcap^{\mathfrak{A}} S = \bigsqcap^{\mathfrak{Z}} S.$

Particularly the above formulas hold for filters on complete lattices.

I’ve added these theorems and their simple consequences to my book.