It is highly unlikely that John moved to the office. It is highly unlikely that Lily is a frog. Chances are slight that Greg is a frog. It is highly unlikely that if either 'Lily is a frog' or 'John moved to the office' but not both then Gertrude is a mouse. It is likely that if either 'Lily is a frog' or 'Greg is a frog' but not both then Mary dropped the apple. It is improbable that if either 'Greg is a frog' or 'John moved to the office' but not both then Julius is a swan.
It is probable that 'Greg is a frog' or 'Lily is a frog' or both.
It is improbable that 'Greg is a frog' or 'Lily is a frog' or both.
It is probable that 'Greg is a frog' or 'Lily is a frog' or 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
  0.05::factA.
  0.05::factB.
  0.1::factC.
  %hop1
  0.05::factX:-xor(factB,factA).
  0.7::factY:-xor(factB,factC).
  0.1::factZ:-xor(factC,factA).

  %hop2
  conclusion:-or(factC,factB).

  query(conclusion).
  
'Greg is a frog' or 'Lily is a frog' or both.