We believe that Greg is a frog. It is certain that Mary got the apple. There is a very good chance that Lily is a rhino. Chances are about even that if 'Greg is a frog' or 'Mary got the apple' or both then Winona is a wolf. There is a very good chance that if 'Mary got the apple and Lily is a rhino' then Brian is yellow. We believe that if either 'Mary got the apple' or 'Lily is a rhino' but not both then Julius is a frog.
There is a very good chance that 'Lily is a rhino' or 'Brian is yellow' or both.
There is a very good chance that 'Lily is a rhino' or 'Brian is yellow' or both.
Chances are slight that 'Lily is a rhino' or 'Brian is yellow' 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
  0.75::factA.
  1.0::factB.
  0.8::factC.
  %hop1
  0.5::factX:-or(factA,factB).
  0.8::factY:-and(factB,factC).
  0.75::factZ:-xor(factB,factC).

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

  query(conclusion).
  
'Lily is a rhino' or 'Brian is yellow' or both.