There is a very good chance that Bernhard is a frog. It is impossible that Brian is a lion. We doubt that Gertrude is a mouse. Chances are about even that if 'Brian is a lion and Bernhard is a frog' then Lily is yellow. It is unlikely that if 'Gertrude is a mouse and Bernhard is a frog' then John left the football. We doubt that if either 'Brian is a lion' or 'Bernhard is a frog' but not both then Greg is a swan.
It is unlikely that 'Greg is a swan' or 'John left the football' or both.
It is unlikely that 'Greg is a swan' or 'John left the football' or both.
It is likely that 'Greg is a swan' or 'John 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
  0.8::factA.
  0.0::factB.
  0.2::factC.
  %hop1
  0.5::factX:-and(factB,factA).
  0.2::factY:-and(factC,factA).
  0.2::factZ:-xor(factB,factA).

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

  query(conclusion).
  
'Greg is a swan' or 'John left the football' or both.