It is impossible that John put down the apple. It is certain that Brian is a swan. It is certain that Gertrude is a mouse. There is a better than even chance that if 'Brian is a swan' or 'Gertrude is a mouse' or both then Bernhard is a frog. Chances are about even that if 'Brian is a swan' or 'John put down the apple' or both then Julius is a lion. We believe that if either 'Brian is a swan' or 'Gertrude is a mouse' but not both then Greg is a rhino.
It is impossible that 'John put down the apple and Greg is a rhino'.
It is impossible that 'John put down the apple and Greg is a rhino'.
It is almost certain that 'John put down the apple and Greg is a rhino'.

  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.
  1.0::factB.
  1.0::factC.
  %hop1
  0.6::factX:-or(factB,factC).
  0.5::factY:-or(factB,factA).
  0.75::factZ:-xor(factB,factC).

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

  query(conclusion).
  
'John put down the apple and Greg is a rhino'.