It is impossible that Lily is yellow. It is highly unlikely that Greg is a frog. There is a better than even chance that Gertrude is a wolf. There is a better than even chance that if either 'Greg is a frog' or 'Lily is yellow' but not both then Julius is gray. It is improbable that if 'Gertrude is a wolf and Lily is yellow' then Sandra dropped the milk. It is almost certain that if 'Lily is yellow and Gertrude is a wolf' then Bernhard is a swan.
We believe that 'Greg is a frog and Sandra dropped the milk'.
It is impossible that 'Greg is a frog and Sandra dropped the milk'.
We believe that 'Greg is a frog and Sandra dropped the milk'.

  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.
  0.05::factB.
  0.6::factC.
  %hop1
  0.6::factX:-xor(factB,factA).
  0.1::factY:-and(factC,factA).
  0.95::factZ:-and(factA,factC).

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

  query(conclusion).
  
'Greg is a frog and Sandra dropped the milk'.