There is little chance that Bernhard is green. It is probable that Greg is a rhino. There is little chance that Brian is yellow. We believe that if either 'Brian is yellow' or 'Bernhard is green' but not both then John moved to the office. There is almost no chance that if 'Greg is a rhino' or 'Brian is yellow' or both then Jeff dropped the apple. It is impossible that if 'Brian is yellow and Bernhard is green' then Sandra left the football.
There is little chance that 'Sandra left the football' or 'Brian is yellow' or both.
There is little chance that 'Sandra left the football' or 'Brian is yellow' or both.
It is almost certain that 'Sandra left the football' or 'Brian is yellow' or both.

  and(A,B) :- A,B.
  or(A,B) :- A;B.
  nand(A,B) :- not(and(A,B)).
  nor(A,B) :- not(or(A,B)).
  xor(A,B) :- or(A,B), nand(A,B).

  %hop0
  0.1::factA.
  0.7::factB.
  0.1::factC.
  %hop1
  0.75::factX:-xor(factC,factA).
  0.02::factY:-or(factB,factC).
  0.0::factZ:-and(factC,factA).

  %hop2
  conclusion:-or(factZ,factC).

  query(conclusion).
  
'Sandra left the football' or 'Brian is yellow' or both.