It is highly likely that Mary discarded the milk. We believe that Greg is a rhino. It is certain that Winona is a mouse. There is a very good chance that if 'Winona is a mouse' or 'Mary discarded the milk' or both then John moved to the office. It is probably not the case that if 'Mary discarded the milk' or 'Greg is a rhino' or both then Julius is a frog. There is little chance that if either 'Greg is a rhino' or 'Winona is a mouse' but not both then Brian is yellow.
It is impossible that 'Brian is yellow and Julius is a frog'.
It is impossible that 'Brian is yellow and Julius is a frog'.
There is a very good chance that 'Brian is yellow and Julius is a frog'.

  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
  0.9::factA.
  0.75::factB.
  1.0::factC.
  %hop1
  0.8::factX:-or(factC,factA).
  0.25::factY:-or(factA,factB).
  0.1::factZ:-xor(factB,factC).

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

  query(conclusion).
  
'Brian is yellow and Julius is a frog'.