There is a very good chance that Greg is a frog. It is likely that Gertrude is a mouse. There is little chance that Lily is white. There is a better than even chance that if either 'Gertrude is a mouse' or 'Greg is a frog' but not both then John got the apple. Chances are slight that if either 'Greg is a frog' or 'Lily is white' but not both then Yann is hungry. It is almost certain that if 'Gertrude is a mouse and Greg is a frog' then Brian is gray.
There is almost no chance that 'Brian is gray' or 'Yann is hungry' or both.
There is a better than even chance that 'Brian is gray' or 'Yann is hungry' or both.
There is almost no chance that 'Brian is gray' or 'Yann is hungry' 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.
  0.7::factB.
  0.1::factC.
  %hop1
  0.6::factX:-xor(factB,factA).
  0.1::factY:-xor(factA,factC).
  0.95::factZ:-and(factB,factA).

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

  query(conclusion).
  
'Brian is gray' or 'Yann is hungry' or both.