There is a very good chance that Lily is yellow. It is probably not the case that Greg is a swan. We doubt that Julius is a rhino. There is little chance that if 'Julius is a rhino and Greg is a swan' then John went to the garden. It is likely that if either 'Julius is a rhino' or 'Lily is yellow' but not both then Mary got the apple. We believe that if either 'Julius is a rhino' or 'Lily is yellow' but not both then Yann is thirsty.
Chances are about even that 'Greg is a swan' or 'Julius is a rhino' or both.
Chances are about even that 'Greg is a swan' or 'Julius is a rhino' or both.
It is impossible that 'Greg is a swan' or 'Julius 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
  0.8::factA.
  0.25::factB.
  0.2::factC.
  %hop1
  0.1::factX:-and(factC,factB).
  0.7::factY:-xor(factC,factA).
  0.75::factZ:-xor(factC,factA).

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

  query(conclusion).
  
'Greg is a swan' or 'Julius is a rhino' or both.