In {HEAD ~ this case}, {TAIL ~ the first single leg grounded period} corresponds to the current single leg grounded period 
In { HEAD ~ this case } , { TAIL ~ the first single leg grounded period } corresponds to the current single leg grounded period
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH