It is likely that Greg is a lion. Chances are slight that Gertrude is a sheep. It is probable that Bill went to the office. We believe that if either 'Greg is a lion' or 'Gertrude is a sheep' but not both then Bernhard is a swan. We believe that if 'Bill went to the office' or 'Greg is a lion' or both then John dropped the apple. It is probable that if 'Greg is a lion' or 'Gertrude is a sheep' or both then Mary left the football.
It is highly unlikely that 'Greg is a lion and John dropped the apple'.
Chances are about even that 'Greg is a lion and John dropped the apple'.
It is highly unlikely that 'Greg is a lion and John dropped the apple'.

  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
  0.7::factA.
  0.1::factB.
  0.7::factC.
  %hop1
  0.75::factX:-xor(factA,factB).
  0.75::factY:-or(factC,factA).
  0.7::factZ:-or(factA,factB).

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

  query(conclusion).
  
'Greg is a lion and John dropped the apple'.