It is probable that John picked up the milk. Chances are about even that Brian is a frog. We believe that Jeff went to the bedroom. It is probably the case that if 'Jeff went to the bedroom' or 'Brian is a frog' or both then Sandra left the milk. We doubt that if 'Jeff went to the bedroom and Brian is a frog' then Bernhard is a lion. There is little chance that if 'John picked up the milk and Jeff went to the bedroom' then Lily is a swan.
It is probably the case that 'Lily is a swan and Sandra left the milk'.
It is highly unlikely that 'Lily is a swan and Sandra left the milk'.
It is probably the case that 'Lily is a swan and Sandra left the milk'.

  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.
  0.5::factB.
  0.75::factC.
  %hop1
  0.7::factX:-or(factC,factB).
  0.2::factY:-and(factC,factB).
  0.1::factZ:-and(factA,factC).

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

  query(conclusion).
  
'Lily is a swan and Sandra left the milk'.