added a fresh_left lemma that contains all instantiation
for the various atom-types.
header {* \chapter{The Rely-Guarantee Method}
\section {Abstract Syntax}
*}
theory RG_Com imports Main begin
text {* Semantics of assertions and boolean expressions (bexp) as sets
of states. Syntax of commands @{text com} and parallel commands
@{text par_com}. *}
types
'a bexp = "'a set"
datatype 'a com =
Basic "'a \<Rightarrow>'a"
| Seq "'a com" "'a com"
| Cond "'a bexp" "'a com" "'a com"
| While "'a bexp" "'a com"
| Await "'a bexp" "'a com"
types 'a par_com = "(('a com) option) list"
end