anchor.diff:          | num_expr mult_op num_expr
           | num_expr plus_op num_expr
           | PAR_OPEN num_expr PAR_CLOSE
  +        | variable
           | NUMBER
           ;
   
  -bool_op: OR | AND | COMMA;
  +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;
   
  -
  -
  -
  -
  
positive.code: 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 */
  
negative.code:          | num_expr eq_op num_expr
           | bool_expr bool_op bool_expr
           | PAR_OPEN bool_expr PAR_CLOSE
           | variable
           | TRUE
           | FALSE
           ;
  