It is probable that Brian is a lion. It is certain that Bernhard is a swan. It is probably the case that Mary dropped the milk. It is impossible that if 'Brian is a lion and Mary dropped the milk' then Gertrude is a sheep. It is highly likely that if 'Mary dropped the milk and Brian is a lion' then Julius is a rhino. It is unlikely that if 'Brian is a lion' or 'Mary dropped the milk' or both then Greg is white.
Chances are about even that 'Brian is a lion and Mary dropped the milk'.
Chances are about even that 'Brian is a lion and Mary dropped the milk'.
It is impossible that 'Brian is a lion and Mary dropped 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.
  1.0::factB.
  0.7::factC.
  %hop1
  0.0::factX:-and(factA,factC).
  0.9::factY:-and(factC,factA).
  0.2::factZ:-or(factA,factC).

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

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