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