5.10 The Complete Concrete Syntax of AS

program     -->   "abstract" "syntax" "of" id 
                     definition
                  "end" [id] ";"
definition  -->   "is" declaration*
                | "extends" id "with" declaration*
declaration -->   operator | inclusion | union | line
operator    -->   id ("," id)* ":" signature ";"
signature   -->   domain "->" id
domain      -->   "string"
                | "integer"
                | "tree"
                | [tid ("#" tid)*]
                | tid "+"
                | tid "*"
                | "(" tid ":" tid "->" tid ")"

inclusion   -->   tid "<" sinclusion ";"
sinclusion  -->   id
                | id "<" sinclusion

union       -->   id "=" tid ("+" tid)* ";"