*To*: isabelle-users Mailinglist <isabelle-users at cl.cam.ac.uk>*Subject*: [isabelle] Variable 'b::{} not of sort type*From*: Gerwin Klein <gerwin.klein at nicta.com.au>*Date*: Wed, 31 Oct 2012 17:14:56 +1100

We recently came across this surprising (to me) behaviour in Isabelle 2012 (also development version): lemma "f x = f x" apply (insert refl[where t="x"]) *** Type unification failed: Variable 'b::{} not of sort type *** *** Failed to meet type constraint: *** *** Term: x :: 'b *** Type: ??'a whereas the workaround lemma "f x = f (x::'b)" apply (insert refl[where t="x"]) works as expected. I would have expected type inference to give 'b the default sort "type" (as it does to 'a, if you look at the output of "term f" with show_sorts on). Am I expecting wrong or should this be changed? Cheers, Gerwin

**Follow-Ups**:**Re: [isabelle] Variable 'b::{} not of sort type***From:*Lars Noschinski

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