There is a better than even chance that Greg is a frog. Chances are about even that Brian is a swan. It is probably not the case that Sandra left the football. It is probable that if 'Brian is a swan' or 'Greg is a frog' or both then Julius is white. There is a very good chance that if 'Greg is a frog' or 'Brian is a swan' or both then Mary went to the bedroom. It is highly unlikely that if either 'Greg is a frog' or 'Sandra left the football' but not both then John picked up the apple.
It is impossible that 'Greg is a frog' or 'Sandra left the football' or both.
It is probable that 'Greg is a frog' or 'Sandra left the football' or both.
It is impossible that 'Greg is a frog' or 'Sandra left the football' 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
  0.6::factA.
  0.5::factB.
  0.25::factC.
  %hop1
  0.7::factX:-or(factB,factA).
  0.8::factY:-or(factA,factB).
  0.05::factZ:-xor(factA,factC).

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

  query(conclusion).
  
'Greg is a frog' or 'Sandra left the football' or both.