We doubt that Brian is yellow. It is highly likely that John left the apple. We believe that Bernhard is a frog. There is little chance that if 'Bernhard is a frog' or 'John left the apple' or both then Mary picked up the apple. It is unlikely that if 'Brian is yellow' or 'John left the apple' or both then Greg is a swan. It is highly unlikely that if 'John left the apple and Brian is yellow' then Jeff went to the bedroom.
It is likely that 'John left the apple and Bernhard is a frog'.
It is likely that 'John left the apple and Bernhard is a frog'.
It is impossible that 'John left the apple and Bernhard 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
  0.2::factA.
  0.9::factB.
  0.75::factC.
  %hop1
  0.1::factX:-or(factC,factB).
  0.2::factY:-or(factA,factB).
  0.05::factZ:-and(factB,factA).

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

  query(conclusion).
  
'John left the apple and Bernhard is a frog'.