It is probably the case that Brian is a rhino. There is a very good chance that John took the apple. Chances are slight that Mary dropped the milk. It is probable that if either 'Brian is a rhino' or 'John took the apple' but not both then Julius is gray. Chances are slight that if either 'Mary dropped the milk' or 'Brian is a rhino' but not both then Greg is a swan. There is little chance that if 'Mary dropped the milk and John took the apple' then Lily is a lion.
It is highly unlikely that 'Mary dropped the milk' or 'Brian is a rhino' or both.
We believe that 'Mary dropped the milk' or 'Brian is a rhino' or both.
It is highly unlikely that 'Mary dropped the milk' or 'Brian is a rhino' 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
  0.7::factA.
  0.8::factB.
  0.1::factC.
  %hop1
  0.7::factX:-xor(factA,factB).
  0.1::factY:-xor(factC,factA).
  0.1::factZ:-and(factC,factB).

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

  query(conclusion).
  
'Mary dropped the milk' or 'Brian is a rhino' or both.