There is a very good chance that Julius is white. It is highly likely that Brian is a swan. Chances are about even that Lily is a frog. It is highly likely that if either 'Brian is a swan' or 'Lily is a frog' but not both then Greg is a lion. It is improbable that if 'Julius is white and Brian is a swan' then Sandra dropped the milk. There is little chance that if 'Lily is a frog and Brian is a swan' then Emily is a mouse.
There is little chance that 'Brian is a swan' or 'Sandra dropped the milk' or both.
It is highly likely that 'Brian is a swan' or 'Sandra dropped the milk' or both.
There is little chance that 'Brian is a swan' or 'Sandra dropped the milk' or both.

  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
  0.8::factA.
  0.9::factB.
  0.5::factC.
  %hop1
  0.9::factX:-xor(factB,factC).
  0.1::factY:-and(factA,factB).
  0.1::factZ:-and(factC,factB).

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

  query(conclusion).
  
'Brian is a swan' or 'Sandra dropped the milk' or both.