We believe that Gertrude is a wolf. It is impossible that Sandra dropped the milk. There is a very good chance that Bernhard is yellow. There is a better than even chance that if 'Sandra dropped the milk' or 'Bernhard is yellow' or both then Brian is a swan. Chances are about even that if 'Bernhard is yellow and Gertrude is a wolf' then John got the apple. It is probable that if either 'Sandra dropped the milk' or 'Bernhard is yellow' but not both then Mary went to the office.
It is impossible that 'Sandra dropped the milk and John got the apple'.
It is impossible that 'Sandra dropped the milk and John got the apple'.
There is a better than even chance that 'Sandra dropped the milk and John got the apple'.

  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
  0.75::factA.
  0.0::factB.
  0.8::factC.
  %hop1
  0.6::factX:-or(factB,factC).
  0.5::factY:-and(factC,factA).
  0.7::factZ:-xor(factB,factC).

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

  query(conclusion).
  
'Sandra dropped the milk and John got the apple'.