It is probably the case that Greg is gray. We doubt that Mary got the football. Chances are about even that Lily is a rhino. We believe that if 'Lily is a rhino and Mary got the football' then Sandra grabbed the apple. There is little chance that if 'Greg is gray' or 'Mary got the football' or both then Jason is tired. It is highly likely that if 'Lily is a rhino and Mary got the football' then John left the milk.
Chances are slight that either 'Jason is tired' or 'Sandra grabbed the apple' but not both.
Chances are slight that either 'Jason is tired' or 'Sandra grabbed the apple' but not both.
It is probable that either 'Jason is tired' or 'Sandra grabbed the apple' but not 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.
  0.2::factB.
  0.5::factC.
  %hop1
  0.75::factX:-and(factC,factB).
  0.1::factY:-or(factA,factB).
  0.9::factZ:-and(factC,factB).

  %hop2
  conclusion:-xor(factY,factX).

  query(conclusion).
  
Either 'Jason is tired' or 'Sandra grabbed the apple' but not both.