It is improbable that Gertrude is a cat. We doubt that Greg is a frog. We believe that Sandra dropped the apple. It is unlikely that if 'Sandra dropped the apple and Greg is a frog' then Emily is a mouse. It is probable that if either 'Gertrude is a cat' or 'Sandra dropped the apple' but not both then Bernhard is a lion. There is almost no chance that if 'Gertrude is a cat and Greg is a frog' then Lily is white.
It is probably not the case that either 'Gertrude is a cat' or 'Greg is a frog' but not both.
It is probably not the case that either 'Gertrude is a cat' or 'Greg is a frog' but not both.
It is probably the case that either 'Gertrude is a cat' or 'Greg is a frog' 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
  0.1::factA.
  0.2::factB.
  0.75::factC.
  %hop1
  0.2::factX:-and(factC,factB).
  0.7::factY:-xor(factA,factC).
  0.02::factZ:-and(factA,factB).

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

  query(conclusion).
  
Either 'Gertrude is a cat' or 'Greg is a frog' but not both.