There is a very good chance that Brian is a frog. It is unlikely that Gertrude is a cat. It is likely that Winona is a sheep. We doubt that if 'Brian is a frog and Winona is a sheep' then Julius is white. There is a better than even chance that if 'Brian is a frog and Winona is a sheep' then Greg is a rhino. It is highly unlikely that if either 'Gertrude is a cat' or 'Brian is a frog' but not both then Bernhard is green.
There is a very good chance that 'Greg is a rhino' or 'Brian is a frog' or both.
There is a very good chance that 'Greg is a rhino' or 'Brian is a frog' or both.
Chances are slight that 'Greg is a rhino' or 'Brian 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
  0.8::factA.
  0.2::factB.
  0.7::factC.
  %hop1
  0.2::factX:-and(factA,factC).
  0.6::factY:-and(factA,factC).
  0.05::factZ:-xor(factB,factA).

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

  query(conclusion).
  
'Greg is a rhino' or 'Brian is a frog' or both.