==== SSE

+ Anon bNodes "_:"

+ test another form -- (debug FOO)

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

+ Var token: needs to include bNode variables.

+ Start a collection of Writers to go with Builders.