anchor.diff:  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
  +  |  t_PLUS t_FILLER? prefix_expr
  +  |  t_MINUS t_FILLER? prefix_expr
     ;
   
   pow_expr :
  
positive.code:   ;
  
  element_list :
       element (element_separator_list element2)*
    ;
  
  element :
       expr_in_array
    ;
  
  element2 :
       expr_in_array2
    ;
  
  //non-empty
  
negative.code: 
  //TODO-AC: antlr periodically has trouble with this (because of unary plus?)
  plus_expr_in_array :
       binary_expr_in_array ((t_FILLER (t_PLUS | t_MINUS) t_FILLER | (t_PLUS | t_MINUS) t_FILLER?) binary_expr_in_array)*
    ;
  
  binary_expr_in_array :
  