There is almost no chance that Sandra dropped the milk. It is highly unlikely that Greg is a rhino. We doubt that John took the apple. We doubt that if either 'John took the apple' or 'Greg is a rhino' but not both then Mary left the football. It is unlikely that if 'John took the apple and Sandra dropped the milk' then Yann is tired. It is improbable that if 'John took the apple and Sandra dropped the milk' then Gertrude is a cat.
It is almost certain that either 'Sandra dropped the milk' or 'Mary left the football' but not both.
It is highly unlikely that either 'Sandra dropped the milk' or 'Mary left the football' but not both.
It is almost certain that either 'Sandra dropped the milk' or 'Mary left the football' 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
  0.02::factA.
  0.05::factB.
  0.2::factC.
  %hop1
  0.2::factX:-xor(factC,factB).
  0.2::factY:-and(factC,factA).
  0.1::factZ:-and(factC,factA).

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

  query(conclusion).
  
Either 'Sandra dropped the milk' or 'Mary left the football' but not both.