digraph example2 {
  GW150914 [ URL="[https://en.wikipedia.org/wiki/First_observation_of_gravitational_waves|Wikipedia Article on GW150914]" ]
  GW151226 [ URL="[https://en.wikipedia.org/wiki/GW151226|Wikipedia Article on GW151226]" ]
  GW170817 [ URL="[https://en.wikipedia.org/wiki/GW170817|Wikipedia Article on GW170817]" ]
  WikiData [ URL="[[SimpleGraph-WikiData]]" ]
  WikiData -> GW150914 
  WikiData -> GW151226 
  WikiData -> GW170817
}