Flights =
[{new_york,paris,123,[mo,tu,we,fr,sa]},
 {paris,new_york,124,[tu,we,th,sa,su]},
 {new_york,london,232,[tu,we,th,fr]},
 {new_york,london,800,[mo,we,fr,sa]},
 {london,new_york,233,[we,th,fr,sa]},
 {london,new_york,801,[tu,th,sa,su]},
 {london,paris,444,[mo,tu,we,th,fr,sa]},
 {paris,london,445,[mo,tu,we,th,fr,sa]}].