Chances are slight that Greg is a rhino. There is a very good chance that Mary went to the office. There is almost no chance that Bernhard is gray. It is impossible that if 'Bernhard is gray' or 'Mary went to the office' or both then Sandra dropped the milk. There is little chance that if 'Mary went to the office and Greg is a rhino' then Brian is yellow. It is probably not the case that if 'Mary went to the office' or 'Bernhard is gray' or both then Lily is a swan.
It is unlikely that 'Bernhard is gray' or 'Lily is a swan' or both.
It is unlikely that 'Bernhard is gray' or 'Lily is a swan' or both.
We believe that 'Bernhard is gray' or 'Lily is a swan' 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
  0.1::factA.
  0.8::factB.
  0.02::factC.
  %hop1
  0.0::factX:-or(factC,factB).
  0.1::factY:-and(factB,factA).
  0.25::factZ:-or(factB,factC).

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

  query(conclusion).
  
'Bernhard is gray' or 'Lily is a swan' or both.