We doubt that Julius is yellow. There is almost no chance that Emily is a cat. It is probable that Greg is a frog. It is certain that if 'Emily is a cat' or 'Greg is a frog' or both then Fred left the football. It is impossible that if 'Emily is a cat' or 'Julius is yellow' or both then John grabbed the apple. It is highly unlikely that if 'Emily is a cat and Greg is a frog' then Brian is yellow.
We doubt that either 'Greg is a frog' or 'John grabbed the apple' but not both.
It is likely that either 'Greg is a frog' or 'John grabbed the apple' but not both.
We doubt that either 'Greg is a frog' or 'John 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
  0.2::factA.
  0.02::factB.
  0.7::factC.
  %hop1
  1.0::factX:-or(factB,factC).
  0.0::factY:-or(factB,factA).
  0.05::factZ:-and(factB,factC).

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

  query(conclusion).
  
Either 'Greg is a frog' or 'John grabbed the apple' but not both.