# [isabelle] Notation issues trying to make Multiset more convenient

Hi,
As you know, {a,b,c} works for sets, and [a,b,c] works for lists.

`I'm in need of this sort of thing for Multisets, but I just can't get it
``to work.
`
Firstly, syntax issues ... anything along the lines of:
translations
"{# x, xs #}" == "{# x #} + {# xs #}"
fails due to a parse error, even if I replace # with any non-bracket symbol.
On the other hand, bracket symbols work:
translations
"[{x, xs}]" == "{# x #} + {# xs #}"
but this redefines the "one set in a list" syntax.

`What I can do is specify some unary operator for multiset_of and pass in
``a list:
` notation
multiset_of ("\<kappa> _" [40] 40)
but then I lose the nice simplification of:
lemma "a :# ({# b #} + {# a #})" by simp
as this won't work:
lemma "a #\<in> \<kappa>[b, a, c]" by simp
I am not sure how to proceed from here. Could you offer any advice?
Sincerely,
Rafal Kolanski.

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