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