AIRPORT
[
LIB_AIRPORT:z  {<choice $z>}
]

LIB_AIRPORT [
  LIB_US_AIRPORT:a
  LIB_INTL_AIRPORT:a
] {return($a)}

LIB_US_AIRPORT [
  AIRPORT_ALBUQUERQUE_ABQ:a
  AIRPORT_ATLANTA_ATL:a
  AIRPORT_AUSTIN_AUS:a
  AIRPORT_BALTIMORE_BWI:a
  AIRPORT_BOSTON_BOS:a
  AIRPORT_CHARLOTTE_CLT:a
  AIRPORT_CHICAGO_MDW:a
  AIRPORT_CHICAGO_ORD:a
  AIRPORT_CINCINNATI_CVG:a
  AIRPORT_CLEVELAND_CLE:a
  AIRPORT_COLUMBUS_CMH:a
  AIRPORT_DALLAS_FORT_WORTH_DFW:a
  AIRPORT_DENVER_DEN:a
  AIRPORT_DETROIT_DTW:a
  AIRPORT_FORT_LAUDERDALE_FLL:a
  AIRPORT_HONOLULU_HNL:a
  AIRPORT_HOUSTON_HOU:a
  AIRPORT_HOUSTON_IAH:a
  AIRPORT_INDIANAPOLIS_IND:a
  AIRPORT_KANSAS_CITY_MCI:a
  AIRPORT_LAS_VEGAS_LAS:a
  AIRPORT_LOS_ANGELES_LAX:a
  AIRPORT_MEMPHIS_MEM:a
  AIRPORT_MIAMI_MIA:a
  AIRPORT_MILWAUKEE_MKE:a
  AIRPORT_MINNEAPOLIS_SAINT_PAUL_MSP:a
  AIRPORT_NASHVILLE_BNA:a
  AIRPORT_NEW_ORLEANS_MSY:a
  AIRPORT_NEW_YORK_JFK:a
  AIRPORT_NEW_YORK_LGA:a
  AIRPORT_NEWARK_EWR:a
  AIRPORT_OAKLAND_OAK:a
  AIRPORT_ONTARIO_ONT:a ; Los Angeles, not Canada.
  AIRPORT_ORLANDO_MCO:a
  AIRPORT_PHILADELPHIA_PHL:a
  AIRPORT_PHOENIX_PHX:a
  AIRPORT_PITTSBURGH_PIT:a
  AIRPORT_PORTLAND_PDX:a
  AIRPORT_RALEIGH_DURHAM_RDU:a
  AIRPORT_SACRAMENTO_SMF:a
  AIRPORT_SAINT_LOUIS_STL:a
  AIRPORT_SALT_LAKE_CITY_SLC:a
  AIRPORT_SAN_ANTONIO_SAT:a
  AIRPORT_SAN_DIEGO_SAN:a
  AIRPORT_SAN_FRANCISCO_SFO:a
  AIRPORT_SAN_JOSE_SJC:a
  AIRPORT_SEATTLE_SEA:a
  AIRPORT_TAMPA_TPA:a
  AIRPORT_TORONTO_YYZ:a
  AIRPORT_WASHINGTON_DCA:a
  AIRPORT_WASHINGTON_IAD:a
  AIRPORT_WEST_PALM_BEACH_PBI:a
] {return($a)}
  
LIB_INTL_AIRPORT [
  AIRPORT_AMSTERDAM_AMS:a
  AIRPORT_ATHENS_ATH:a
  AIRPORT_AUCKLAND_AKL:a
  AIRPORT_BANGKOK_BKK:a
  AIRPORT_BARCELONA_BCN:a
  AIRPORT_BEIJING_PEK:a
  AIRPORT_BERLIN_TXL:a
  AIRPORT_BOMBAY_BOM:a
  AIRPORT_BRISBANE_BNE:a
  AIRPORT_BRUSSELS_BRU:a
  AIRPORT_CAIRO_CAI:a
  AIRPORT_CALGARY_YYC:a
  AIRPORT_COPENHAGEN_CPH:a
  AIRPORT_DUBAI_DXB:a
  AIRPORT_DUBLIN_DUB:a
  AIRPORT_DUSSELDORF_DUS:a
  AIRPORT_FRANKFURT_FRA:a
  AIRPORT_HAMBURG_HAM:a
  AIRPORT_HELSINKI_HEL:a
  AIRPORT_HONG_KONG_HKG:a
  AIRPORT_ISTANBUL_IST:a
  AIRPORT_JAKARTA_CGK:a
  AIRPORT_JOHANNESBURG_JNB:a
  AIRPORT_KUALA_LUMPUR_KUL:a
  AIRPORT_LISBON_LIS:a
  AIRPORT_LONDON_LGW:a
  AIRPORT_LONDON_LHR:a
  AIRPORT_MADRID_MAD:a
  AIRPORT_MALAGA_AGP:a
  AIRPORT_MANCHESTER_MAN:a
  AIRPORT_MANILA_MNL:a
  AIRPORT_MELBOURNE_MEL:a
  AIRPORT_MEXICO_CITY_MEX:a
  AIRPORT_MILAN_LIN:a
  AIRPORT_MONTREAL_YUL:a
  AIRPORT_MOSCOW_SVO:a
  AIRPORT_MUNICH_MUC:a
  AIRPORT_NAGOYA_NGO:a
  AIRPORT_NEW_DELHI_DEL:a
  AIRPORT_NICE_NCE:a
  AIRPORT_OSAKA_KIX:a
  AIRPORT_PARIS_CDG:a
  AIRPORT_PUSAN_PUS:a
  AIRPORT_RIO_DE_JANEIRO_GIG:a
  AIRPORT_RIYADH_RUH:a
  AIRPORT_ROME_FCO:a
  AIRPORT_SAN_JUAN_SJU:a
  AIRPORT_SAO_PAULO_GRU:a
  AIRPORT_SAPPORO_CTS:a
  AIRPORT_SEOUL_SEL:a
  AIRPORT_SHANGHAI_SHA:a
  AIRPORT_SINGAPORE_SIN:a
  AIRPORT_STOCKHOLM_ARN:a
  AIRPORT_STUTTGART_STR:a
  AIRPORT_SYDNEY_SYD:a
  AIRPORT_TAIPEI_TPE:a
  AIRPORT_TEL_AVIV_TLV:a
  AIRPORT_TOKYO_NRT:a
  AIRPORT_VANCOUVER_YVR:a
  AIRPORT_VIENNA_VIE:a
  AIRPORT_ZURICH_ZRH:a
] {return($a)}

AIRPORT_ALBUQUERQUE_ABQ [
  ( albuquerque ?( new mexico ) ?SUB_INTL_AIRPORT )
] {return("ABQ")}

AIRPORT_ATLANTA_ATL [
  ( ?hartsfield atlanta ?georgia ?SUB_INTL_AIRPORT )
  ( atlanta hartsfield ?SUB_INTL_AIRPORT )
  ( hartsfield ?SUB_INTL_AIRPORT )
  ( a t l ?atlanta )
  ( atlanta a t l )
] {return("ATL")}

AIRPORT_AUSTIN_AUS [
  ( austin ?texas ?bergstrom [ ?SUB_MUNI_AIRPORT ?SUB_INTL_AIRPORT ] )
] {return("AUS")}

AIRPORT_BALTIMORE_BWI [
  ( baltimore ?maryland ?washington ?SUB_INTL_AIRPORT )
  ( b w i )
  ( baltimore b w i )
  ( b w i baltimore )
] {return("BWI")}

AIRPORT_BOSTON_BOS [
  ( boston ?massachusetts ?logan ?SUB_INTL_AIRPORT )
  ( ?boston logan ?SUB_INTL_AIRPORT )
] {return("BOS")}

AIRPORT_CHARLOTTE_CLT [
  ( douglas ?( north carolina ) ?SUB_INTL_AIRPORT )
] {return("CLT")}

AIRPORT_CHICAGO_MDW [
  ( chicago ?illinois midway ?airport )

  ; NOTE: To prevent an ambiguity with Chicago O'Hare, the speaker must
  ; say at least "chicago midway".  If they say only "chicago", the grammar 
  ; will return "ORD" (O'Hare), which is often the desired result.  An
  ; alternative would be to return both, and let the application ask
  ; which one the caller wants.  If this is what you prefer, then 
  ; uncomment the following line:
  ; ( chicago ?illinois )
] {return("MDW")}

AIRPORT_CHICAGO_ORD [
  ( chicago ?o'hare ?illinois ?SUB_INTL_AIRPORT )
  ( o'hare ?chicago ?SUB_INTL_AIRPORT )
  ( o r d )
] {return("ORD")}

AIRPORT_CINCINNATI_CVG [
  ( cincinnati ?ohio ?SUB_INTL_AIRPORT )
] {return("CVG")}

AIRPORT_CLEVELAND_CLE [
  ( cleveland ?ohio ?SUB_INTL_AIRPORT )
] {return("CLE")}

AIRPORT_COLUMBUS_CMH [
  ( columbus ?ohio ?SUB_INTL_AIRPORT )
] {return("CMH")}

AIRPORT_DALLAS_FORT_WORTH_DFW [
  ( dallas ?( fort worth ) ?texas ?SUB_INTL_AIRPORT )
] {return("DFW")}

AIRPORT_DENVER_DEN [
  ( denver ?colorado ?SUB_INTL_AIRPORT )
] {return("DEN")}

AIRPORT_DETROIT_DTW [
  ( detroit ?michigan ?SUB_METRO_AIRPORT )
] {return("DTW")}

AIRPORT_FORT_LAUDERDALE_FLL [
  ( fort lauderdale ?florida ?SUB_INTL_AIRPORT )
] {return("FLL")}

AIRPORT_HONOLULU_HNL [
  ( honolulu ?hawaii ?airport )
] {return("HNL")}

AIRPORT_HOUSTON_HOU [

  ; NOTE: The speaker must say at least "houston hobby"
  ; to prevent an ambiguity with Houston Intercontinental.
  ( houston ?texas hobby ?airport )
] {return("HOU")}

AIRPORT_HOUSTON_IAH [
  ( houston ?texas ?SUB_INTL_AIRPORT )
  ( houston ?texas intercontinental ?airport )
] {return("IAH")}

AIRPORT_INDIANAPOLIS_IND [
  ( indianapolis ?indiana ?airport )
] {return("IND")}

AIRPORT_KANSAS_CITY_MCI [
  ( kansas city ?missouri ?SUB_INTL_AIRPORT )

  ; NOTE: Even though the airport code is MCI, many people call this 
  ; airport "KCI"
  ( k c i )
] {return("MCI")}

AIRPORT_LAS_VEGAS_LAS [
  ( ?las vegas ?nevada ?SUB_INTL_AIRPORT )
] {return("LAS")}

AIRPORT_LOS_ANGELES_LAX [
  ( los angeles ?california ?SUB_INTL_AIRPORT )
  ( l a )
  ( l a x )
  ( l a x los angeles )
  ( los angeles l a x )
] {return("LAX")}

AIRPORT_MEMPHIS_MEM [
  ( memphis ?tennessee ?SUB_INTL_AIRPORT )
] {return("MEM")}

AIRPORT_MIAMI_MIA [
  ( miami ?florida ?SUB_INTL_AIRPORT )
] {return("MIA")}

AIRPORT_MILWAUKEE_MKE [
  ( milwaukee ?wisconsin ?SUB_INTL_AIRPORT )
] {return("MKE")}

AIRPORT_MINNEAPOLIS_SAINT_PAUL_MSP [
  ( minneapolis ?( saint paul ) ?minnesota ?SUB_INTL_AIRPORT )
  ( saint paul ?minneapolis ?minnesota ?SUB_INTL_AIRPORT )
] {return("MSP")}

AIRPORT_NASHVILLE_BNA [
  ( nashville ?tennessee ?SUB_METRO_AIRPORT )
] {return("BNA")}

AIRPORT_NEW_ORLEANS_MSY [
  ( new orleans ?louisiana ?SUB_INTL_AIRPORT )
] {return("MSY")}

AIRPORT_NEW_YORK_JFK [
  ( [ ( new york kennedy )
      ( kennedy )
      ( new york ?city j f k )
      ( j f k ?( new york ?city ) )
      ( john f kennedy )
      ( j f k kennedy )
    ] ?SUB_INTL_AIRPORT
  )

  ; NOTE: The following generates an ambiguity with LGA (LaGuardia)
  ( new york ?city ?( new york) ?SUB_INTL_AIRPORT)
] {return("JFK")}

AIRPORT_NEW_YORK_LGA [
  ( [ ( new york ?city laguardia )
      ( laguardia )
      ( laguardia new york ?city )
    ] ?SUB_INTL_AIRPORT
  )

  ; NOTE: The following generates an ambiguity with JFK
  ( new york ?city ?( new york ) ?SUB_INTL_AIRPORT )
] {return("LGA")}

AIRPORT_NEWARK_EWR [
  ( newark ?( new jersey ) ?SUB_INTL_AIRPORT )
  ( e w r )
] {return("EWR")}

AIRPORT_OAKLAND_OAK [
  ( oakland ?california ?SUB_INTL_AIRPORT )
] {return("OAK")}

AIRPORT_ONTARIO_ONT [

  ; NOTE: Suburban Los Angeles, not in Canada.
  ( ontario ?california ?SUB_INTL_AIRPORT )
] {return("ONT")}

AIRPORT_ORLANDO_MCO [
  ( orlando ?florida ?SUB_INTL_AIRPORT )
] {return("MCO")}

AIRPORT_PHILADELPHIA_PHL [
  ( philadelphia ?pennsylvania ?SUB_INTL_AIRPORT )
] {return("PHL")}

AIRPORT_PHOENIX_PHX [
  ( phoenix ?arizona ?SUB_INTL_AIRPORT )
] {return("PHX")}

AIRPORT_PITTSBURGH_PIT [
  ( pittsburgh ?pennsylvania ?SUB_INTL_AIRPORT )
  ( p i t )
  ( pit )
] {return("PIT")}

AIRPORT_PORTLAND_PDX [
  ( portland ?oregon ?SUB_INTL_AIRPORT )
] {return("PDX")}

AIRPORT_RALEIGH_DURHAM_RDU [
  ( [ ( raleigh ?durham ) ( durham ) ] ?( north carolina ) ?SUB_INTL_AIRPORT )
  ( r d u )
] {return("RDU")}

AIRPORT_SACRAMENTO_SMF [
  ( sacramento ?california ?SUB_METRO_AIRPORT )
] {return("SMF")}

AIRPORT_SAINT_LOUIS_STL [
  ( saint louis ?missouri ?SUB_INTL_AIRPORT )
] {return("STL")}

AIRPORT_SALT_LAKE_CITY_SLC [
  ( salt lake ?city ?utah ?SUB_INTL_AIRPORT )
  ( s l c )
] {return("SLC")}

AIRPORT_SAN_ANTONIO_SAT [
  ( san antonio ?texas ?SUB_INTL_AIRPORT )
] {return("SAT")}

AIRPORT_SAN_DIEGO_SAN [
  ( san diego ?california ?SUB_INTL_AIRPORT )
] {return("SAN")}

AIRPORT_SAN_FRANCISCO_SFO [
  ( [ ( san francisco ) ( san fran ) frisco ] ?california ?SUB_INTL_AIRPORT )
  ( s f o )
  ( san francisco s f o )
] {return("SFO")}

AIRPORT_SAN_JOSE_SJC [
  ( san jose ?california ?SUB_INTL_AIRPORT )
] {return("SJC")}

AIRPORT_SEATTLE_SEA [
  ( [ ( seattle ?tacoma ) tacoma  ( sea tack ) ] 
    ?washington ?SUB_INTL_AIRPORT 
  )
] {return("SEA")}

AIRPORT_TAMPA_TPA [
  ( SUB_TAMPA ?florida ?SUB_INTL_AIRPORT )
] {return("TPA")}

AIRPORT_WASHINGTON_DCA [
  ( washington national )
  ( ?ronald reagan SUB_DC ?national ?airport )
  ( ?ronald reagan ?SUB_DC national )
  ( national ?airport ?SUB_DC )
  ( reagan national ?airport ?SUB_DC )
  ( d c a ?washington ?national )
  ( ?SUB_DC d c a )
  ( ?SUB_DC ?ronald reagan )

  ; NOTE: The following generates an ambiguity with Washington Dulles
  SUB_DC
] {return("DCA")}

AIRPORT_WASHINGTON_IAD [
 ( washington ?dulles ?SUB_INTL_AIRPORT )
 ( dulles SUB_DC )
 ( SUB_DC dulles )
 ( i a d )

 ; NOTE: The following generates an ambiguity with Washington National
 SUB_DC
] {return("IAD")}

AIRPORT_WEST_PALM_BEACH_PBI [
  ( west palm ?beach ?florida ?SUB_INTL_AIRPORT )
] {return("PBI")}

; International Airport Grammars

AIRPORT_AMSTERDAM_AMS [
  ( amsterdam ?[ holland ( ?the netherlands ) ] ?SUB_INTL_AIRPORT )
] {return("AMS")}

AIRPORT_ATHENS_ATH [
  ( athens ?greece ?SUB_INTL_AIRPORT )
] {return("ATH")}

AIRPORT_AUCKLAND_AKL [
  ( auckland ?(new zealand) ?SUB_INTL_AIRPORT )  
] {return("AKL")}

AIRPORT_BANGKOK_BKK [
  ( bangkok ?thailand ?SUB_INTL_AIRPORT )
] {return("BKK")}

AIRPORT_BARCELONA_BCN [
  ( barcelona ?spain ?SUB_INTL_AIRPORT )  
] {return("BCN")}

AIRPORT_BEIJING_PEK [
  ( [ beijing peking ] ?china ?SUB_INTL_AIRPORT )  
] {return("PEK")}

AIRPORT_BERLIN_TXL [
  ( [ berlin ] ?germany ?SUB_INTL_AIRPORT )
] {return("TXL")}

AIRPORT_BOMBAY_BOM [
  ( bombay ?india ?SUB_INTL_AIRPORT )
] {return("BOM")}

AIRPORT_BRISBANE_BNE [
  ( brisbane ?australia ?SUB_INTL_AIRPORT )
] {return("BNE")}

AIRPORT_BRUSSELS_BRU [
  ( brussels ?belgium ?SUB_INTL_AIRPORT )
] {return("BRU")}

AIRPORT_CAIRO_CAI [
  ( cairo ?egypt ?SUB_INTL_AIRPORT )
] {return("CAI")}

AIRPORT_CALGARY_YYC [
  ( calgary ?SUB_INTL_AIRPORT ?alberta ?canada )
] {return("YYC")}

AIRPORT_COPENHAGEN_CPH [
  ( copenhagen ?denmark ?SUB_INTL_AIRPORT )  
] {return("CPH")}

AIRPORT_DUBAI_DXB [
  ( dubai ?[ (united arab emirates) (u a e) ] ?SUB_INTL_AIRPORT )
] {return("DXB")}

AIRPORT_DUBLIN_DUB [
  ( dublin ?( ?( republic of ) ireland ) ?SUB_INTL_AIRPORT )
] {return("DUB")}

AIRPORT_DUSSELDORF_DUS [
  ( dusseldorf ?germany ?SUB_INTL_AIRPORT )
] {return("DUS")}

AIRPORT_FRANKFURT_FRA [
  ( frankfurt ?germany ?SUB_INTL_AIRPORT )
] {return("FRA")}

AIRPORT_HAMBURG_HAM [
  ( hamburg ?germany ?SUB_INTL_AIRPORT )
] {return("HAM")}

AIRPORT_HELSINKI_HEL [
  ( helsinki ?finland ?SUB_INTL_AIRPORT )
] {return("HEL")}

AIRPORT_HONG_KONG_HKG [
  ( hong kong ?china ?SUB_INTL_AIRPORT )
] {return("HKG")}

AIRPORT_ISTANBUL_IST [
  ( istanbul ?turkey ?SUB_INTL_AIRPORT )  
] {return("IST")}

AIRPORT_JAKARTA_CGK [
  ( jakarta ?indonesia ?SUB_INTL_AIRPORT )  
] {return("CGK")}

AIRPORT_JOHANNESBURG_JNB [
  ( johannesburg ?(south africa) ?SUB_INTL_AIRPORT )
] {return("JNB")}

AIRPORT_KUALA_LUMPUR_KUL [
  ( kuala lumpur ?malaysia ?SUB_INTL_AIRPORT )  
] {return("KUL")}

AIRPORT_LISBON_LIS [
  ( lisbon ?portugal ?SUB_INTL_AIRPORT)
] {return("LIS")}

AIRPORT_LONDON_LGW [
  ( ?london gatwick ?SUB_ENGLAND ?SUB_INTL_AIRPORT )
  ( gatwick ?SUB_INTL_AIRPORT london ?SUB_ENGLAND )

  ; NOTE: The following generates an ambiguity with London Heathrow
  ( london ?SUB_ENGLAND ?SUB_INTL_AIRPORT )
] {return("LGW")}

AIRPORT_LONDON_LHR [
  ( ?london heathrow ?SUB_ENGLAND ?SUB_INTL_AIRPORT )
  ( heathrow ?SUB_INTL_AIRPORT london ?SUB_ENGLAND )
  
  ; NOTE: The following generates an ambiguity with London Gatwick
  ( london ?SUB_ENGLAND ?SUB_INTL_AIRPORT )
] {return("LHR")}

AIRPORT_MADRID_MAD [
  ( madrid ?spain ?SUB_INTL_AIRPORT )
] {return("MAD")}

AIRPORT_MALAGA_AGP [
  ( malaga ?spain ?SUB_INTL_AIRPORT )
] {return("AGP")}

AIRPORT_MANCHESTER_MAN [
  ( manchester ?SUB_ENGLAND ?SUB_INTL_AIRPORT )
] {return("MAN")}

AIRPORT_MANILA_MNL [
  ( manila ?(?the philippines) ?SUB_INTL_AIRPORT )
] {return("MNL")}

AIRPORT_MELBOURNE_MEL [
  ( melbourne ?australia ?SUB_INTL_AIRPORT )    
] {return("MEL")}

AIRPORT_MEXICO_CITY_MEX [
  ( mexico city ?mexico ?SUB_INTL_AIRPORT )
] {return("MEX")}

AIRPORT_MILAN_LIN [
  ( milan ?italy ?SUB_INTL_AIRPORT )
] {return("LIN")}

AIRPORT_MONTREAL_YUL [
  ( montreal ?canada ?SUB_INTL_AIRPORT )
] {return("YUL")}

AIRPORT_MOSCOW_SVO [
  ( moscow ?russia ?SUB_INTL_AIRPORT )
] {return("SVO")}

AIRPORT_MUNICH_MUC [
  ( munich ?germany ?SUB_INTL_AIRPORT )
] {return("MUC")}

AIRPORT_NAGOYA_NGO [
  ( nagoya ?japan ?SUB_INTL_AIRPORT )
] {return("NGO")}

AIRPORT_NEW_DELHI_DEL [
  ( ?new delhi ?india ?SUB_INTL_AIRPORT )
] {return("DEL")}

AIRPORT_NICE_NCE [
  ( nice ?france ?SUB_INTL_AIRPORT )
] {return("NCE")}

AIRPORT_OSAKA_KIX [
  ( osaka ?japan ?SUB_INTL_AIRPORT )  
  ( kansai ?japan ?SUB_INTL_AIRPORT )  
  ( k i x )
] {return("KIX")}

AIRPORT_PARIS_CDG [
  ( paris ?france ?charles de gaulle ?SUB_INTL_AIRPORT )
  ( ?charles de gaulle ?SUB_INTL_AIRPORT )
  ( paris ?france )
] {return("CDG")}

AIRPORT_PUSAN_PUS [
  ( pusan ?( ?south korea ) ?SUB_INTL_AIRPORT )
] {return("PUS")}

AIRPORT_RIO_DE_JANEIRO_GIG [
  ( rio ?( de janeiro ) ?brazil ?SUB_INTL_AIRPORT )
] {return("GIG")}

AIRPORT_RIYADH_RUH [
  ( riyadh ?( saudi arabia ) ?SUB_INTL_AIRPORT )
] {return("RUH")}

AIRPORT_ROME_FCO [
  ( rome ?italy ?SUB_INTL_AIRPORT )
] {return("FCO")}

AIRPORT_SAN_JUAN_SJU [
  ( san juan ?( puerto rico ) ?SUB_INTL_AIRPORT )
] {return("SJU")}

AIRPORT_SAO_PAULO_GRU [
  ( sao paulo ?brazil ?SUB_INTL_AIRPORT )
] {return("GRU")}

AIRPORT_SAPPORO_CTS [
  ( sapporo ?japan ?SUB_INTL_AIRPORT )
] {return("CTS")}

AIRPORT_SEOUL_SEL [
  ( seoul ?( ?south korea ) ?SUB_INTL_AIRPORT )
] {return("SEL")}

AIRPORT_SHANGHAI_SHA [
  ( shanghai ?china ?SUB_INTL_AIRPORT )
] {return("SHA")}

AIRPORT_SINGAPORE_SIN [
  ( singapore ?SUB_INTL_AIRPORT )
] {return("SIN")}

AIRPORT_STOCKHOLM_ARN [
  ( stockholm ?sweden ?SUB_INTL_AIRPORT )
] {return("ARN")}

AIRPORT_STUTTGART_STR [
  ( stuttgart ?germany ?SUB_INTL_AIRPORT )
] {return("STR")}

AIRPORT_SYDNEY_SYD [
  ( sydney ?australia ?SUB_INTL_AIRPORT )
] {return("SYD")}

AIRPORT_TAIPEI_TPE [
  ( taipei ?taiwan ?SUB_INTL_AIRPORT )
] {return("TPE")}

AIRPORT_TEL_AVIV_TLV [
  ( tel aviv ?israel ?SUB_INTL_AIRPORT )
] {return("TLV")}

AIRPORT_TOKYO_NRT [
  ( [ ( tokyo ?narita ) ( narita ?tokyo ) ] ?japan ?SUB_INTL_AIRPORT )  
] {return("NRT")}

AIRPORT_TORONTO_YYZ [
  ( toronto ?ontario ?canada ?SUB_INTL_AIRPORT )
] {return("YYZ")}

AIRPORT_VANCOUVER_YVR [
  ( vancouver ?[ ( british columbia ) ( b c ) ] ?canada ?SUB_INTL_AIRPORT )
] {return("YVR")}

AIRPORT_VIENNA_VIE [
  ( vienna ?austria ?SUB_INTL_AIRPORT )
] {return("VIE")}

AIRPORT_ZURICH_ZRH [
  ( zurich ?switzerland ?SUB_INTL_AIRPORT )
] {return("ZRH")}

; Airport helper grammars

SUB_INTL_AIRPORT [
  international 
  airport
  ( international airport )
]
 
SUB_METRO_AIRPORT [
  metro
  metropolitan
  airport
  ( metropolitan airport )
  ( metro airport )
]
 
SUB_MUNI_AIRPORT [
  municipal
  airport
  ( municipal airport )
]
 
SUB_ENGLAND [
 england
 ( united kingdom )
 ( great britain )
 ( u k )
]

SUB_TAMPA [
  ( tampa ?bay )
  ( tampa ?bay saint petersburg )
  ( tampa ?bay saint pete )
  ( saint petersburg )
  ( saint pete )
]

SUB_DC [
  washington
  ( washington d c )
  ( d c )
]