It is probably not the case that Greg is a lion. It is probable that Brian is green. There is a better than even chance that Lily is a frog. There is a better than even chance that if either 'Brian is green' or 'Greg is a lion' but not both then John went to the office. It is likely that if 'Lily is a frog' or 'Greg is a lion' or both then Jessica is a cat. It is unlikely that if either 'Greg is a lion' or 'Brian is green' but not both then Mary left the football.
Chances are about even that either 'John went to the office' or 'Greg is a lion' but not both.
Chances are about even that either 'John went to the office' or 'Greg is a lion' but not both.
It is highly unlikely that either 'John went to the office' or 'Greg is a lion' 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
  0.25::factA.
  0.7::factB.
  0.6::factC.
  %hop1
  0.6::factX:-xor(factB,factA).
  0.7::factY:-or(factC,factA).
  0.2::factZ:-xor(factA,factB).

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

  query(conclusion).
  
Either 'John went to the office' or 'Greg is a lion' but not both.