<?xml version="1.0" ?>
<sdf version="1.5">
  <world name="default">
    <physics type="ode">
      <gravity>0 0 0</gravity>
    </physics>
    <include>
      <uri>model://sun</uri>
    </include>

    <include>
      <uri>model://multilink_nested</uri>
    </include>

  </world>
</sdf>
