The backframe is configured by interlinked linkages such that the backframe can be locked in a fully extended position in use, or be collapsible when not in use in a way that {HEAD ~ the overall dimension} of the collapsible backframe is smaller than {TAIL ~ the fully extended backframe} 
is smaller than
The backframe is configured by interlinked linkages such that the backframe can be locked in a fully extended position in use , or be collapsible when not in use in a way that { HEAD ~ the overall dimension } of the collapsible backframe is smaller than { TAIL ~ the fully extended backframe }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL