docs: public static double distance(double p1lat, double p1lon, double p2lat, double p2lon) {
          return RADIUS
                          * Math.acos(makeDoubleInRange(Math.sin(p1lat) * Math.sin(p2lat)
            + Math.cos(p1lat) * Math.cos(p2lat)
            * Math.cos(p2lon - p1lon)));
      }