 if {HEAD ~ the version} of {TAIL ~ the current node} corresponds to the stored map version at the step , matching node coordinates with the stored map and extracting corresponding nodes; and 
of
if { HEAD ~ the version } of { TAIL ~ the current node } corresponds to the stored map version at the step , matching node coordinates with the stored map and extracting corresponding nodes ; and
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH