It is probably the case that Brian is green. There is little chance that Lily is a swan. There is a very good chance that Mary grabbed the milk. It is unlikely that if 'Mary grabbed the milk and Lily is a swan' then Gertrude is a cat. There is a better than even chance that if 'Brian is green and Lily is a swan' then Daniel dropped the apple. We doubt that if either 'Lily is a swan' or 'Brian is green' but not both then Jason is bored.
It is impossible that 'Lily is a swan and Jason is bored'.
It is impossible that 'Lily is a swan and Jason is bored'.
It is certain that 'Lily is a swan and Jason is bored'.

  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
  0.7::factA.
  0.1::factB.
  0.8::factC.
  %hop1
  0.2::factX:-and(factC,factB).
  0.6::factY:-and(factA,factB).
  0.2::factZ:-xor(factB,factA).

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

  query(conclusion).
  
'Lily is a swan and Jason is bored'.