discontinued special treatment of structure Ast: no pervasive content, no inclusion in structure Syntax;
no_document use_thys [
"~~/src/HOL/Library/Countable",
"~~/src/HOL/Library/Monad_Syntax",
"~~/src/HOL/Library/Code_Natural",
"~~/src/HOL/Library/LaTeXsugar"];
use_thys ["Imperative_HOL_ex"];