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