There is a better than even chance that John grabbed the apple. We believe that Greg is a lion. It is probable that Bernhard is yellow. It is probably not the case that if 'Greg is a lion and John grabbed the apple' then Julius is a frog. We doubt that if either 'Greg is a lion' or 'John grabbed the apple' but not both then Lily is a rhino. It is unlikely that if either 'John grabbed the apple' or 'Greg is a lion' but not both then Sandra dropped the milk.
It is certain that 'John grabbed the apple and Julius is a frog'.
It is improbable that 'John grabbed the apple and Julius is a frog'.
It is certain that 'John grabbed the apple and Julius 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
  0.6::factA.
  0.75::factB.
  0.7::factC.
  %hop1
  0.25::factX:-and(factB,factA).
  0.2::factY:-xor(factB,factA).
  0.2::factZ:-xor(factA,factB).

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

  query(conclusion).
  
'John grabbed the apple and Julius is a frog'.