replaced Thm.legacy_freezeT by Thm.unvarify_global -- these facts stem from closed definitions, i.e. there are no term Vars;
theory Syntax
imports Base
begin
chapter {* Concrete syntax and type-checking *}
text FIXME
section {* Parsing and printing *}
text FIXME
section {* Checking and unchecking \label{sec:term-check} *}
end