anchor.diff:        FLOAT_TYPE_SUFFIX?
       ;
   
  -SYMBOLIC_NAME
  +CONSTANT_STR 
       : ([a-zA-Z] | [0-9] | '_') ([a-zA-Z] | [0-9] | '_')* ('\'')*
  -    | '"'  (ESCAPE_SEQUENCE | ~('\\' | '"' ) )* '"'
  +    ;
  +
  +QUOTED_CONSTANT_STR
  +    : '"'  (ESCAPE_SEQUENCE | ~('\\' | '"' ) )* '"'
       | '\'' (ESCAPE_SEQUENCE | ~('\\' | '\'') )* '\''
       ;
   
  
positive.code: ON                      : 'on' ;
  IN                      : 'in' ;
  // Special Functions
  CARTESIAN_PRODUCT       : 'x' ;
  FUNCTION_TYPE           : '->' ;
  // Logic Operators
  IMPLICATION             : '=>' ;
  
negative.code: UNDERSCORE              : '_' ;
  PERIOD                  : '.' ;
  
  INTEGER 
      : ('0'..'9')+
      ;
      
  RATIONAL
      : ('0' | '1'..'9' '0'..'9'*)
      | ('0'..'9')+ '.' ('0'..'9')+ EXPONENT? FLOAT_TYPE_SUFFIX?
  