flight(from(name(lhr), city(london)), to(name(bsl), city(basel)),
       day(tuesday)).

flight(from(name(bsl), city(basel)), to(name(cdg), city(paris)),
       day(tuesday)).

flight(from(name(bsl), city(basel)), to(name(jfk), city(new_york)),
       day(tuesday)).

flight(from(name(cdg), city(paris)), to(name(nor), city(norwich)),
       day(tuesday)).

flight(from(name(jfk), city(new_york)), to(name(bsl), city(basel)),
       day(wednesday)).

flight(from(name(bsl), city(basel)), to(name(nor), city(norwich)),
       day(wednesday)).

flight(from(name(nor), city(norwich)), to(name(cdg), city(paris)),
       day(wednesday)).