We believe that Brian is yellow. It is highly likely that Emily is a mouse. It is improbable that Daniel dropped the apple. We believe that if 'Brian is yellow and Emily is a mouse' then Greg is yellow. Chances are slight that if either 'Brian is yellow' or 'Emily is a mouse' but not both then Lily is white. It is unlikely that if 'Emily is a mouse and Daniel dropped the apple' then Julius is gray.
Chances are about even that either 'Lily is white' or 'Greg is yellow' but not both.
Chances are about even that either 'Lily is white' or 'Greg is yellow' but not both.
It is impossible that either 'Lily is white' or 'Greg is yellow' 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
  0.75::factA.
  0.9::factB.
  0.1::factC.
  %hop1
  0.75::factX:-and(factA,factB).
  0.1::factY:-xor(factA,factB).
  0.2::factZ:-and(factB,factC).

  %hop2
  conclusion:-xor(factY,factX).

  query(conclusion).
  
Either 'Lily is white' or 'Greg is yellow' but not both.