It is highly likely that Brian is white. It is probably not the case that Greg is a rhino. It is unlikely that Mary left the milk. We doubt that if 'Mary left the milk and Greg is a rhino' then Gertrude is a sheep. There is a better than even chance that if 'Brian is white' or 'Mary left the milk' or both then Bill went to the office. It is highly unlikely that if 'Brian is white' or 'Greg is a rhino' or both then John picked up the milk.
It is impossible that 'Gertrude is a sheep and Brian is white'.
It is impossible that 'Gertrude is a sheep and Brian is white'.
It is highly likely that 'Gertrude is a sheep and Brian is white'.

  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
  0.9::factA.
  0.25::factB.
  0.2::factC.
  %hop1
  0.2::factX:-and(factC,factB).
  0.6::factY:-or(factA,factC).
  0.05::factZ:-or(factA,factB).

  %hop2
  conclusion:-and(factX,factA).

  query(conclusion).
  
'Gertrude is a sheep and Brian is white'.