It is probably not the case that John went to the garden. It is highly unlikely that Brian is a lion. It is probably the case that Gertrude is a sheep. It is highly likely that if 'John went to the garden' or 'Gertrude is a sheep' or both then Bernhard is yellow. Chances are slight that if either 'Gertrude is a sheep' or 'Brian is a lion' but not both then Daniel dropped the milk. Chances are about even that if 'Brian is a lion and John went to the garden' then Lily is a frog.
It is certain that 'Lily is a frog' or 'Brian is a lion' or both.
It is highly unlikely that 'Lily is a frog' or 'Brian is a lion' or both.
It is certain that 'Lily is a frog' or 'Brian is a lion' 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
  0.25::factA.
  0.05::factB.
  0.7::factC.
  %hop1
  0.9::factX:-or(factA,factC).
  0.1::factY:-xor(factC,factB).
  0.5::factZ:-and(factB,factA).

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

  query(conclusion).
  
'Lily is a frog' or 'Brian is a lion' or both.