It is impossible that Greg is a lion. It is probably not the case that Mary got the milk. We believe that John put down the milk. It is improbable that if 'Greg is a lion and Mary got the milk' then Brian is a frog. It is probably not the case that if either 'Greg is a lion' or 'Mary got the milk' but not both then Sandra left the apple. We believe that if 'Greg is a lion' or 'John put down the milk' or both then Julius is yellow.
Chances are about even that 'Mary got the milk and Brian is a frog'.
It is impossible that 'Mary got the milk and Brian is a frog'.
Chances are about even that 'Mary got the milk and Brian 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
  0.0::factA.
  0.25::factB.
  0.75::factC.
  %hop1
  0.1::factX:-and(factA,factB).
  0.25::factY:-xor(factA,factB).
  0.75::factZ:-or(factA,factC).

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

  query(conclusion).
  
'Mary got the milk and Brian is a frog'.