anchor.diff:  // NOTE that NAND/NOR are in (...)* now (used to be in (...)?).
   // (21.1.2004, e.f.)
   expression
  -  : relation ( options{greedy=true;}: logical_operator relation )*
  +  : relation ( : logical_operator relation )*
     ;
   
   factor
  -  : primary ( options{greedy=true;}: DOUBLESTAR primary )?
  +  : primary ( : DOUBLESTAR primary )?
     | ABS primary
     | NOT primary
     ;
  
positive.code: // `a op -b' - use `a op (-b)' instead).
  // (3.2.2004, e.f.)
  simple_expression
    : ( PLUS | MINUS )? term ( options{greedy=true;}: adding_operator term )*
    ;
  
  simple_simultaneous_statement
  
negative.code:   ;
  
  physical_literal
    : abstract_literal (: identifier)
    ;
  
  physical_type_definition
  