There is a better than even chance that Greg is a frog. It is unlikely that John took the football. There is almost no chance that Gertrude is a sheep. It is certain that if 'John took the football and Greg is a frog' then Brian is white. There is a very good chance that if either 'Greg is a frog' or 'Gertrude is a sheep' but not both then Mary picked up the milk. There is almost no chance that if either 'Greg is a frog' or 'Gertrude is a sheep' but not both then Lily is a swan.
It is probably the case that either 'Greg is a frog' or 'Mary picked up the milk' but not both.
There is little chance that either 'Greg is a frog' or 'Mary picked up the milk' but not both.
It is probably the case that either 'Greg is a frog' or 'Mary picked up the milk' but not both.

  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.
  0.2::factB.
  0.02::factC.
  %hop1
  1.0::factX:-and(factB,factA).
  0.8::factY:-xor(factA,factC).
  0.02::factZ:-xor(factA,factC).

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

  query(conclusion).
  
Either 'Greg is a frog' or 'Mary picked up the milk' but not both.