doc-src/Intro/list.thy

added worker_group;
fork: default to subgroup of worker_group;
removed obsolete fork_local;
join/get_result: cumulative flattened exceptions;
map: subgroup of worker_group;

List = FOL +
types 	list 1
arities list	:: (term)term
consts	Nil	:: "'a list"
   	Cons	:: "['a, 'a list] => 'a list" 
end