Re: [Haskell-cafe] Is there a name for this algebraic structure?

On Tue, Apr 21, 2015 at 02:51:16PM +1200, Richard A. O'Keefe wrote:

You said in words that

...

Every S can be reconstructed from a sequence of updates:

but your formula

...

forall s. exists [a]. s == foldl update empty [a]

says that a (not necessarily unique) sequence of updates can be reconstructed from every S. I think you meant something like "there are no elements of S but those that can be constructed by a sequence of updates".

Those sound like the same thing to me!