It is probable that Sandra took the football. Chances are about even that Jason is tired. Chances are slight that John dropped the apple. It is highly likely that if 'John dropped the apple' or 'Sandra took the football' or both then Bernhard is a rhino. We believe that if either 'John dropped the apple' or 'Sandra took the football' but not both then Greg is a frog. There is little chance that if 'Sandra took the football and Jason is tired' then Lily is a lion.
Chances are about even that either 'Sandra took the football' or 'Jason is tired' but not both.
Chances are about even that either 'Sandra took the football' or 'Jason is tired' but not both.
It is almost certain that either 'Sandra took the football' or 'Jason is tired' 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.
  0.5::factB.
  0.1::factC.
  %hop1
  0.9::factX:-or(factC,factA).
  0.75::factY:-xor(factC,factA).
  0.1::factZ:-and(factA,factB).

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

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