It is impossible that Gertrude is a sheep. It is improbable that Greg is a rhino. It is probably not the case that Mary went to the office. It is likely that if either 'Greg is a rhino' or 'Gertrude is a sheep' but not both then Lily is yellow. There is a very good chance that if 'Mary went to the office and Gertrude is a sheep' then John grabbed the milk. We doubt that if either 'Mary went to the office' or 'Greg is a rhino' but not both then Bernhard is a lion.
It is impossible that 'Lily is yellow and Gertrude is a sheep'.
It is impossible that 'Lily is yellow and Gertrude is a sheep'.
Chances are about even that 'Lily is yellow and Gertrude is a sheep'.

  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
  0.0::factA.
  0.1::factB.
  0.25::factC.
  %hop1
  0.7::factX:-xor(factB,factA).
  0.8::factY:-and(factC,factA).
  0.2::factZ:-xor(factC,factB).

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

  query(conclusion).
  
'Lily is yellow and Gertrude is a sheep'.