It is probably not the case that Greg is a swan. It is impossible that Fred is in the cinema. It is impossible that John discarded the milk. It is probable that if either 'Fred is in the cinema' or 'Greg is a swan' but not both then Brian is green. It is probably not the case that if 'Greg is a swan and Fred is in the cinema' then Mary got the football. There is little chance that if either 'Fred is in the cinema' or 'Greg is a swan' but not both then Julius is yellow.
It is probably not the case that 'Brian is green' or 'Greg is a swan' or both.
It is probably not the case that 'Brian is green' or 'Greg is a swan' or both.
It is probable that 'Brian is green' or 'Greg is a swan' or 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.
  0.0::factB.
  0.0::factC.
  %hop1
  0.7::factX:-xor(factB,factA).
  0.25::factY:-and(factA,factB).
  0.1::factZ:-xor(factB,factA).

  %hop2
  conclusion:-or(factX,factA).

  query(conclusion).
  
'Brian is green' or 'Greg is a swan' or both.