doc-src/Intro/list.thy

added incremental extension functions: extend_log_types, extend_type_gram,
extend_const_gram, extend_consts, extend_trfuns, extend_trrules;
replaced merge by merge_syntaxes;
various minor internal changes;

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