anchor.diff:  edge_label_gen: EDGE_LABEL_TOKEN COLON label (COMMA label)* EOL;
   
   /* Define and rename a label */
  -// TO DO de label moet toch een string zijn?
   label: STRING (RENAME_TOKEN ID)?;
   
   /* Implicative clauses */
  
positive.code:          | num_expr eq_op num_expr
           | bool_expr bool_op bool_expr
           | PAR_OPEN bool_expr PAR_CLOSE
           | TRUE
           | FALSE
           ;
  
negative.code:         | num_expr mult_op num_expr
          | num_expr plus_op num_expr
          | PAR_OPEN num_expr PAR_CLOSE
          | variable
          | NUMBER
          ;
  
  bool_op: COMMA | AND | OR;
  eq_op: EQ | NQ | GT | LT | GE | LE;
  
  pow_op: POW;
  mult_op: MULT | DIV | MOD;
  plus_op: PLUS | MINUS;
  
  