It is impossible that Jeff left the apple. There is a better than even chance that Mary dropped the milk. There is little chance that Brian is a swan. It is probably not the case that if 'Mary dropped the milk and Brian is a swan' then Emily is a sheep. Chances are about even that if 'Mary dropped the milk and Brian is a swan' then John took the football. There is almost no chance that if either 'Mary dropped the milk' or 'Jeff left the apple' but not both then Bernhard is a rhino.
It is certain that 'Mary dropped the milk and Brian is a swan'.
It is highly unlikely that 'Mary dropped the milk and Brian is a swan'.
It is certain that 'Mary dropped the milk and Brian 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
  0.0::factA.
  0.6::factB.
  0.1::factC.
  %hop1
  0.25::factX:-and(factB,factC).
  0.5::factY:-and(factB,factC).
  0.02::factZ:-xor(factB,factA).

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

  query(conclusion).
  
'Mary dropped the milk and Brian is a swan'.