It is probable that Winona is a sheep. Chances are slight that Mary went to the office. We believe that John took the apple. It is unlikely that if either 'John took the apple' or 'Mary went to the office' but not both then Brian is a lion. We doubt that if either 'Mary went to the office' or 'Winona is a sheep' but not both then Sandra dropped the milk. It is highly unlikely that if 'John took the apple and Winona is a sheep' then Greg is white.
It is probable that 'Greg is white' or 'Winona is a sheep' or both.
It is probable that 'Greg is white' or 'Winona is a sheep' or both.
It is impossible that 'Greg is white' or 'Winona is a sheep' 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
  0.7::factA.
  0.1::factB.
  0.75::factC.
  %hop1
  0.2::factX:-xor(factC,factB).
  0.2::factY:-xor(factB,factA).
  0.05::factZ:-and(factC,factA).

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

  query(conclusion).
  
'Greg is white' or 'Winona is a sheep' or both.