It is impossible that Bernhard is a frog. There is a very good chance that Yann is thirsty. It is highly unlikely that Mary went to the hallway. It is probably not the case that if 'Bernhard is a frog and Mary went to the hallway' then Greg is a lion. Chances are slight that if 'Yann is thirsty and Bernhard is a frog' then Daniel dropped the apple. It is unlikely that if 'Bernhard is a frog and Mary went to the hallway' then Julius is yellow.
It is impossible that 'Mary went to the hallway and Julius is yellow'.
It is impossible that 'Mary went to the hallway and Julius is yellow'.
We believe that 'Mary went to the hallway and Julius is yellow'.

  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
  0.0::factA.
  0.8::factB.
  0.05::factC.
  %hop1
  0.25::factX:-and(factA,factC).
  0.1::factY:-and(factB,factA).
  0.2::factZ:-and(factA,factC).

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

  query(conclusion).
  
'Mary went to the hallway and Julius is yellow'.