It is improbable that Greg is green. It is impossible that Brian is a swan. There is little chance that Julius is a frog. There is little chance that if 'Greg is green and Brian is a swan' then John got the milk. It is highly unlikely that if either 'Julius is a frog' or 'Brian is a swan' but not both then Emily is a mouse. It is likely that if 'Brian is a swan and Julius is a frog' then Bernhard is a swan.
There is little chance that either 'Bernhard is a swan' or 'Julius is a frog' but not both.
There is little chance that either 'Bernhard is a swan' or 'Julius is a frog' but not both.
It is highly likely that either 'Bernhard is a swan' or 'Julius is a frog' 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
  0.1::factA.
  0.0::factB.
  0.1::factC.
  %hop1
  0.1::factX:-and(factA,factB).
  0.05::factY:-xor(factC,factB).
  0.7::factZ:-and(factB,factC).

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

  query(conclusion).
  
Either 'Bernhard is a swan' or 'Julius is a frog' but not both.