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