There is little chance that Greg is a frog. It is unlikely that Jason is tired. Chances are about even that Gertrude is a mouse. It is probably not the case that if either 'Greg is a frog' or 'Jason is tired' but not both then John got the apple. It is probably not the case that if 'Greg is a frog and Jason is tired' then Lily is a swan. We believe that if either 'Jason is tired' or 'Greg is a frog' but not both then Brian is a frog.
There is almost no chance that 'Gertrude is a mouse' or 'Brian is a frog' or both.
There is a better than even chance that 'Gertrude is a mouse' or 'Brian is a frog' or both.
There is almost no chance that 'Gertrude is a mouse' or 'Brian is a frog' 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
  0.1::factA.
  0.2::factB.
  0.5::factC.
  %hop1
  0.25::factX:-xor(factA,factB).
  0.25::factY:-and(factA,factB).
  0.75::factZ:-xor(factB,factA).

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

  query(conclusion).
  
'Gertrude is a mouse' or 'Brian is a frog' or both.