It is probable that Bernhard is a swan. It is probably the case that Lily is a frog. It is highly likely that John went to the garden. It is almost certain that if 'John went to the garden and Lily is a frog' then Jeff discarded the milk. It is certain that if 'Bernhard is a swan' or 'Lily is a frog' or both then Brian is white. It is unlikely that if 'John went to the garden' or 'Lily is a frog' or both then Julius is gray.
It is highly unlikely that 'Julius is gray' or 'Lily is a frog' or both.
We believe that 'Julius is gray' or 'Lily is a frog' or both.
It is highly unlikely that 'Julius is gray' or 'Lily 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
  0.7::factA.
  0.7::factB.
  0.9::factC.
  %hop1
  0.95::factX:-and(factC,factB).
  1.0::factY:-or(factA,factB).
  0.2::factZ:-or(factC,factB).

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

  query(conclusion).
  
'Julius is gray' or 'Lily is a frog' or both.