anchor.diff:     | unsignedConstant
      | set
      | NOT factor
  +   | bool
      ;
   
   unsignedConstant
  
positive.code:    ;
  
  
  WS
     : [ \t\r\n] -> skip
     ;
  
negative.code:    : '\'' ('\'\'' | ~ ('\''))* '\''
     ;
  
  
  NUM_INT
     : ('0' .. '9') +
     ;
  
  
  NUM_REAL
     : ('0' .. '9') + (('.' ('0' .. '9') + (EXPONENT)?)? | EXPONENT)
  