Chances are slight that Greg is yellow. It is impossible that Bernhard is a frog. It is unlikely that Jeff went to the bedroom. There is a better than even chance that if 'Jeff went to the bedroom and Bernhard is a frog' then Sandra took the football. Chances are about even that if either 'Greg is yellow' or 'Bernhard is a frog' but not both then Mary left the milk. Chances are slight that if 'Bernhard is a frog and Jeff went to the bedroom' then Brian is white.
There is a better than even chance that 'Brian is white' or 'Bernhard is a frog' or both.
It is impossible that 'Brian is white' or 'Bernhard is a frog' or both.
There is a better than even chance that 'Brian is white' or 'Bernhard is a frog' 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
  0.1::factA.
  0.0::factB.
  0.2::factC.
  %hop1
  0.6::factX:-and(factC,factB).
  0.5::factY:-xor(factA,factB).
  0.1::factZ:-and(factB,factC).

  %hop2
  conclusion:-or(factZ,factB).

  query(conclusion).
  
'Brian is white' or 'Bernhard is a frog' or both.