Chances are about even that Brian is green. It is highly unlikely that Bill got the milk there. We doubt that Emily is a sheep. It is probable that if 'Brian is green' or 'Emily is a sheep' or both then Sandra dropped the milk. It is highly unlikely that if either 'Emily is a sheep' or 'Brian is green' but not both then Bernhard is yellow. Chances are about even that if 'Brian is green' or 'Emily is a sheep' or both then John grabbed the apple.
It is impossible that 'Bernhard is yellow and Emily is a sheep'.
It is impossible that 'Bernhard is yellow and Emily is a sheep'.
There is a better than even chance that 'Bernhard is yellow and Emily 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
  0.5::factA.
  0.05::factB.
  0.2::factC.
  %hop1
  0.7::factX:-or(factA,factC).
  0.05::factY:-xor(factC,factA).
  0.5::factZ:-or(factA,factC).

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

  query(conclusion).
  
'Bernhard is yellow and Emily is a sheep'.