an external output unit configured to output a signal of contents including {HEAD ~ an image} to said {TAIL ~ second wearable display}, and 
to
an external output unit configured to output a signal of contents including { HEAD ~ an image } to said { TAIL ~ second wearable display } , and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH