There is little chance that John discarded the apple. It is highly unlikely that Bernhard is gray. Chances are about even that Jessica is a sheep. It is highly likely that if either 'Jessica is a sheep' or 'John discarded the apple' but not both then Brian is green. There is a better than even chance that if 'Jessica is a sheep' or 'Bernhard is gray' or both then Jeff moved to the office. It is probably the case that if 'Bernhard is gray' or 'Jessica is a sheep' or both then Greg is a frog.
It is almost certain that 'John discarded the apple' or 'Greg is a frog' or both.
Chances are about even that 'John discarded the apple' or 'Greg is a frog' or both.
It is almost certain that 'John discarded the apple' or 'Greg is a frog' or 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.
  0.05::factB.
  0.5::factC.
  %hop1
  0.9::factX:-xor(factC,factA).
  0.6::factY:-or(factC,factB).
  0.7::factZ:-or(factB,factC).

  %hop2
  conclusion:-or(factA,factZ).

  query(conclusion).
  
'John discarded the apple' or 'Greg is a frog' or both.