==== SSE

+ Words/Symbol
  QNames could be Item/words?  Decide on 

+ Builder tidying and testing
  
  ItemLists : cons cells?!
    Why?  Why not?

+ Expr: (exists (pattern ...))
  
+  (group (vars) aggregate)
  
+  Assignment:
  (assign ((?x expr) (?y expr)) --  (:= ?x expr) [is this SELECT/project?]
     (project ...))
     (project (?x ?y (?z expr)) ...)

+ Prefix writing.