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: 
  //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 binary_expr_in_array | (t_PLUS | t_MINUS) t_FILLER? binary_expr_in_array)*
    ;
  
  binary_expr_in_array :
  
negative.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 :
  