There is a very good chance that Bernhard is a swan. We doubt that Julius is white. There is a better than even chance that Fred went to the office. There is a very good chance that if either 'Julius is white' or 'Bernhard is a swan' but not both then Brian is a frog. There is almost no chance that if 'Julius is white and Fred went to the office' then Greg is a lion. It is improbable that if 'Fred went to the office and Bernhard is a swan' then John moved to the garden.
We believe that 'Brian is a frog and Greg is a lion'.
It is impossible that 'Brian is a frog and Greg is a lion'.
We believe that 'Brian is a frog and Greg is a lion'.

  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
  0.8::factA.
  0.2::factB.
  0.6::factC.
  %hop1
  0.8::factX:-xor(factB,factA).
  0.02::factY:-and(factB,factC).
  0.1::factZ:-and(factC,factA).

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

  query(conclusion).
  
'Brian is a frog and Greg is a lion'.