@@ -49,7 +49,7 @@ Next, we define \emph{fancy updates}, which are essentially the same as the basi

Here, $\mask_1$ and $\mask_2$ are the \emph{masks} of the view update, defining which invariants have to be (at least!) available before and after the update.

Masks are sets of natural numbers, \ie they are subsets of $\mathbb{N}$.%

\footnote{Actually, in the Coq development masks are restricted to a class of sets of natural numbers that contains all finite sets and is closed under union, intersection, difference and complement.

The restriction is necessary for engineering reasons to still obtain representation independence: two masks should be \emph{definitionally} equal iff they contain the same invariant names.}

The restriction is necessary for engineering reasons to still obtain representation independence: two masks should be \emph{propositionally} equal iff they contain the same invariant names.}

We use $\top$ as symbol for the largest possible mask, $\nat$, and $\bot$ for the smallest possible mask $\emptyset$.

We will write $\pvs[\mask]\prop$ for $\pvs[\mask][\mask]\prop$.