Chances are about even that Bernhard is a swan. Chances are about even that John dropped the milk. Chances are about even that Greg is white. It is likely that if 'Bernhard is a swan' or 'John dropped the milk' or both then Sandra got the milk. It is highly unlikely that if either 'John dropped the milk' or 'Bernhard is a swan' but not both then Mary went to the office. There is a very good chance that if 'Bernhard is a swan and Greg is white' then Lily is a rhino.
There is almost no chance that 'Mary went to the office and Bernhard is a swan'.
There is almost no chance that 'Mary went to the office and Bernhard is a swan'.
It is likely that 'Mary went to the office and Bernhard is a swan'.

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

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

  query(conclusion).
  
'Mary went to the office and Bernhard is a swan'.