AIRLINE
[
LIB_AIRLINE:z {<choice $z>}
]

LIB_AIRLINE [
  LIB_US_AIRLINE:a
  LIB_INTL_AIRLINE:a
] {return($a)}

LIB_US_AIRLINE [              
  ( [ alaska alaskan ] ?[ air airlines ] ) {return("AS")}
  ( america west ?[ airlines express ] ) {return("HP")}
  ( [ ( american ) ( a m r ) ( american eagle ) ] ?airlines ) {return("AA")}
  ( delta ?[ airlines connection ] ) {return("DL")}
  ( northwest ?airlines ) {return("NW")}
  ( southwest ?airlines ) {return("WN")}
  ( united ?airlines ) {return("UA")}
  ( [ ( u s air ) ( u s ) ( u s airways ) ] ?express ) {return("US")}
  [ ( trans world ?express ?airlines ) ( t w a ) ] {return("TW")}
]
                  
LIB_INTL_AIRLINE [
  ( air canada ) {return("AC")}
  ( air france ) {return("AF")}
  ( all nippon ?airways ) {return("NH")}
  ( british [ air airways airline airlines ] ) {return("BA")}
  ( canadian ?[ air airlines ] ?international ) {return("CP")}
  ( japan ?airlines ) {return("JL")}
  ( k l m ?airlines ) {return("KL")}
  lufthansa {return("LH")}
  ( qantas ?[ airlines airways ] ) {return("QF")}
  [ ( scandinavian ?airlines ?system ) ( s a s ) ] {return("SK")}
  ( singapore ?airlines ) {return("SQ")}
  ( swissair ?airlines ) {return("SR")}
]