There is a very good chance that Greg is a lion. It is probably the case that Brian is a frog. We believe that Bernhard is a swan. We believe that if 'Brian is a frog' or 'Bernhard is a swan' or both then John picked up the apple. It is impossible that if 'Bernhard is a swan and Greg is a lion' then Sandra dropped the milk. There is a very good chance that if 'Greg is a lion' or 'Bernhard is a swan' or both then Mary went to the office.
There is almost no chance that 'Bernhard is a swan' or 'John picked up the apple' or both.
It is highly likely that 'Bernhard is a swan' or 'John picked up the apple' or both.
There is almost no chance that 'Bernhard is a swan' or 'John picked up the apple' 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.
  0.75::factC.
  %hop1
  0.75::factX:-or(factB,factC).
  0.0::factY:-and(factC,factA).
  0.8::factZ:-or(factA,factC).

  %hop2
  conclusion:-or(factC,factX).

  query(conclusion).
  
'Bernhard is a swan' or 'John picked up the apple' or both.