There is a very good chance that Greg is a swan. It is likely that Jessica is a cat. It is highly likely that John got the milk. It is likely that if 'Greg is a swan' or 'John got the milk' or both then Emily is a sheep. There is a very good chance that if either 'Jessica is a cat' or 'John got the milk' but not both then Brian is yellow. It is highly unlikely that if 'Greg is a swan and John got the milk' then Mary went to the garden.
There is little chance that 'Emily is a sheep' or 'Brian is yellow' or both.
There is a very good chance that 'Emily is a sheep' or 'Brian is yellow' or both.
There is little chance that 'Emily is a sheep' or 'Brian is yellow' 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
  0.8::factA.
  0.7::factB.
  0.9::factC.
  %hop1
  0.7::factX:-or(factA,factC).
  0.8::factY:-xor(factB,factC).
  0.05::factZ:-and(factA,factC).

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

  query(conclusion).
  
'Emily is a sheep' or 'Brian is yellow' or both.