It is unlikely that Bernhard is a frog. Chances are about even that Gertrude is a sheep. It is probably not the case that Mary dropped the apple. It is probably not the case that if 'Gertrude is a sheep' or 'Bernhard is a frog' or both then Jeff went to the hallway. It is probably not the case that if 'Gertrude is a sheep' or 'Bernhard is a frog' or both then John moved to the garden. Chances are slight that if 'Bernhard is a frog' or 'Gertrude is a sheep' or both then Jessica is a cat.
It is highly unlikely that either 'Jessica is a cat' or 'Gertrude is a sheep' but not both.
Chances are about even that either 'Jessica is a cat' or 'Gertrude is a sheep' but not both.
It is highly unlikely that either 'Jessica is a cat' or 'Gertrude is a sheep' 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
  0.2::factA.
  0.5::factB.
  0.25::factC.
  %hop1
  0.25::factX:-or(factB,factA).
  0.25::factY:-or(factB,factA).
  0.1::factZ:-or(factA,factB).

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

  query(conclusion).
  
Either 'Jessica is a cat' or 'Gertrude is a sheep' but not both.