It is probably the case that Brian is white. It is highly likely that Greg is a swan. There is almost no chance that Bill went to the kitchen. It is improbable that if 'Bill went to the kitchen and Greg is a swan' then Mary got the football. It is probable that if either 'Brian is white' or 'Greg is a swan' but not both then Gertrude is a sheep. There is little chance that if either 'Greg is a swan' or 'Brian is white' but not both then Lily is green.
There is a better than even chance that 'Mary got the football and Gertrude is a sheep'.
It is impossible that 'Mary got the football and Gertrude is a sheep'.
There is a better than even chance that 'Mary got the football 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
  0.7::factA.
  0.9::factB.
  0.02::factC.
  %hop1
  0.1::factX:-and(factC,factB).
  0.7::factY:-xor(factA,factB).
  0.1::factZ:-xor(factB,factA).

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

  query(conclusion).
  
'Mary got the football and Gertrude is a sheep'.