It is unlikely that Mary left the milk. It is probably the case that Jeff went to the garden. Chances are slight that John discarded the apple. There is a very good chance that if 'Jeff went to the garden' or 'John discarded the apple' or both then Greg is a lion. There is little chance that if 'Mary left the milk and John discarded the apple' then Lily is green. There is a very good chance that if either 'Jeff went to the garden' or 'Mary left the milk' but not both then Julius is gray.
We doubt that 'Jeff went to the garden' or 'Mary left the milk' or both.
We believe that 'Jeff went to the garden' or 'Mary left the milk' or both.
We doubt that 'Jeff went to the garden' or 'Mary left 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
  0.2::factA.
  0.7::factB.
  0.1::factC.
  %hop1
  0.8::factX:-or(factB,factC).
  0.1::factY:-and(factA,factC).
  0.8::factZ:-xor(factB,factA).

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

  query(conclusion).
  
'Jeff went to the garden' or 'Mary left the milk' or both.