We believe that Bernhard is a swan. There is little chance that Gertrude is a mouse. It is probable that Greg is gray. It is certain that if 'Bernhard is a swan' or 'Greg is gray' or both then Lily is white. It is highly unlikely that if 'Greg is gray' or 'Gertrude is a mouse' or both then John moved to the office. It is likely that if either 'Greg is gray' or 'Gertrude is a mouse' but not both then Mary got the apple.
It is certain that 'Mary got the apple and Greg is gray'.
Chances are about even that 'Mary got the apple and Greg is gray'.
It is certain that 'Mary got the apple and Greg is gray'.

  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
  0.75::factA.
  0.1::factB.
  0.7::factC.
  %hop1
  1.0::factX:-or(factA,factC).
  0.05::factY:-or(factC,factB).
  0.7::factZ:-xor(factC,factB).

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

  query(conclusion).
  
'Mary got the apple and Greg is gray'.