# Re: [isabelle] what the meaning of the set's operation `` ?

ÓÎÕä wrote:
> The following are the part of context in dfs.thy.
> ----------------------------------------------------------------
> subsection "Definition of Graphs"
> typedecl node
> types graph = "(node * node) list"
> consts
> nexts :: "[graph, node] \<Rightarrow> node list"
> primrec
> "nexts [] n = []"
> "nexts (e#es) n = (if fst e = n then snd e # nexts es n else nexts es n)"
> definition
> nextss :: "[graph, node list] \<Rightarrow> node set" where
> "nextss g xs = set g `` set xs"
> -----------------------------------------------------------------------
> I don't know the meaning of the operation `` in the "nextss g xs = set g `` set xs"?
> yucy
>
The infix `` is the image of a relation over a set. It is defined in
Relation.thy.
Regards
Tobias

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