anchor.diff:  
   //TODO-AC: antlr periodically has trouble with this (because of unary plus?)
   plus_expr :
  -     binary_expr //(t_FILLER? (t_PLUS | t_MINUS) t_FILLER? binary_expr)*
  +     binary_expr (t_FILLER? (t_PLUS | t_MINUS) t_FILLER? binary_expr)*
     ;
   
   binary_expr :
  
positive.code: prefix_arg :
       pow_arg
    |  t_NOT t_FILLER? prefix_arg
    |  t_PLUS t_FILLER? prefix_arg
    |  t_MINUS t_FILLER? prefix_arg
    ;
  
  pow_arg :
  
negative.code: prefix_expr :
       pow_expr
    |  t_NOT t_FILLER? prefix_expr
    |  (t_PLUS | t_MINUS) t_FILLER? prefix_expr //NB: plus_expr breaks if this is written as two rules
    ;
  
  pow_expr :
  