It is probably not the case that Winona is a mouse. We believe that Fred left the football. Chances are slight that Mary went to the bedroom. It is improbable that if either 'Fred left the football' or 'Winona is a mouse' but not both then Greg is a lion. It is likely that if 'Mary went to the bedroom and Fred left the football' then Julius is a frog. It is probable that if either 'Mary went to the bedroom' or 'Fred left the football' but not both then Lily is green.
It is impossible that either 'Winona is a mouse' or 'Lily is green' but not both.
Chances are about even that either 'Winona is a mouse' or 'Lily is green' but not both.
It is impossible that either 'Winona is a mouse' or 'Lily is green' but not 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
  0.25::factA.
  0.75::factB.
  0.1::factC.
  %hop1
  0.1::factX:-xor(factB,factA).
  0.7::factY:-and(factC,factB).
  0.7::factZ:-xor(factC,factB).

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

  query(conclusion).
  
Either 'Winona is a mouse' or 'Lily is green' but not both.