= Preframe tensor product
{title2=$P\mathbin{\#}Q$}
The tensor represents maps $P\times Q\to R$ preserving finite meets and directed joins in each variable separately. Its pure generators $p\#q$ satisfy the corresponding relations in each variable. The unit is the free <preframe> on one generator, the bottom of the <frame> of truth values. For <frames>, this tensor is their <coproduct>, with $p\#q=i(p)\vee j(q)$; it must not be confused with the rectangle $i(p)\wedge j(q)$.
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