means for receiving {TAIL ~ a knowledge sheet} serving as an alternate solution when computation of said knowledge sheets of {HEAD ~ the scenario} is a failure, 
means for receiving { TAIL ~ a knowledge sheet } serving as an alternate solution when computation of said knowledge sheets of { HEAD ~ the scenario } is a failure ,
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH