means for executing said knowledge sheets serving as said {HEAD ~ alternative solutions} when execution of knowledge sheets is a failure and knowledge sheets serving as {TAIL ~ alternative solutions} are specified to knowledge sheets 
means for executing said knowledge sheets serving as said { HEAD ~ alternative solutions } when execution of knowledge sheets is a failure and knowledge sheets serving as { TAIL ~ alternative solutions } are specified to knowledge sheets
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH