It is highly unlikely that Greg is yellow. It is highly likely that Julius is a swan. It is probably not the case that Gertrude is a sheep. There is little chance that if either 'Gertrude is a sheep' or 'Greg is yellow' but not both then Mary went to the bedroom. It is probable that if 'Greg is yellow' or 'Julius is a swan' or both then Fred is in the office. It is almost certain that if either 'Greg is yellow' or 'Julius is a swan' but not both then Bill left the football.
It is highly likely that 'Fred is in the office and Gertrude is a sheep'.
We doubt that 'Fred is in the office and Gertrude is a sheep'.
It is highly likely that 'Fred is in the office and Gertrude is a sheep'.

  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.
  0.9::factB.
  0.25::factC.
  %hop1
  0.1::factX:-xor(factC,factA).
  0.7::factY:-or(factA,factB).
  0.95::factZ:-xor(factA,factB).

  %hop2
  conclusion:-and(factY,factC).

  query(conclusion).
  
'Fred is in the office and Gertrude is a sheep'.