It is certain that Bernhard is a frog. There is little chance that Greg is green. There is little chance that Jeff went to the bedroom. It is probable that if 'Greg is green and Jeff went to the bedroom' then Jessica is a mouse. There is little chance that if either 'Greg is green' or 'Bernhard is a frog' but not both then Brian is a rhino. Chances are slight that if 'Jeff went to the bedroom' or 'Bernhard is a frog' or both then Mary dropped the milk.
We believe that 'Greg is green' or 'Mary dropped the milk' or both.
It is unlikely that 'Greg is green' or 'Mary dropped the milk' or both.
We believe that 'Greg is green' or 'Mary dropped the milk' 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
  1.0::factA.
  0.1::factB.
  0.1::factC.
  %hop1
  0.7::factX:-and(factB,factC).
  0.1::factY:-xor(factB,factA).
  0.1::factZ:-or(factC,factA).

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

  query(conclusion).
  
'Greg is green' or 'Mary dropped the milk' or both.