It is highly unlikely that Emily is a sheep. It is probably the case that Fred is in the school. It is unlikely that Mary went to the office. There is little chance that if either 'Emily is a sheep' or 'Mary went to the office' but not both then Lily is white. There is a very good chance that if 'Mary went to the office and Emily is a sheep' then John grabbed the apple. It is probably the case that if 'Fred is in the school' or 'Mary went to the office' or both then Greg is a swan.
It is impossible that either 'Lily is white' or 'Greg is a swan' but not both.
Chances are about even that either 'Lily is white' or 'Greg is a swan' but not both.
It is impossible that either 'Lily is white' or 'Greg is a swan' 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
  0.05::factA.
  0.7::factB.
  0.2::factC.
  %hop1
  0.1::factX:-xor(factA,factC).
  0.8::factY:-and(factC,factA).
  0.7::factZ:-or(factB,factC).

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

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