It is highly unlikely that Jessica is a mouse. Chances are about even that Brian is yellow. There is little chance that Greg is green. It is probably not the case that if 'Greg is green' or 'Jessica is a mouse' or both then Gertrude is a sheep. Chances are slight that if 'Greg is green' or 'Jessica is a mouse' or both then John went to the office. It is improbable that if either 'Brian is yellow' or 'Jessica is a mouse' but not both then Bernhard is a frog.
It is highly unlikely that 'Greg is green' or 'Brian is yellow' or both.
There is a better than even chance that 'Greg is green' or 'Brian is yellow' or both.
It is highly unlikely that 'Greg is green' 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
  0.05::factA.
  0.5::factB.
  0.1::factC.
  %hop1
  0.25::factX:-or(factC,factA).
  0.1::factY:-or(factC,factA).
  0.1::factZ:-xor(factB,factA).

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

  query(conclusion).
  
'Greg is green' or 'Brian is yellow' or both.