It is highly unlikely that John went to the office. We doubt that Brian is a frog. It is certain that Mary left the apple. It is probable that if either 'John went to the office' or 'Brian is a frog' but not both then Julius is a lion. It is highly likely that if 'Brian is a frog and John went to the office' then Greg is white. There is a very good chance that if 'John went to the office and Brian is a frog' then Bernhard is a swan.
It is improbable that 'Mary left the apple' or 'Julius is a lion' or both.
It is certain that 'Mary left the apple' or 'Julius is a lion' or both.
It is improbable that 'Mary left the apple' or 'Julius is a lion' 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.
  0.2::factB.
  1.0::factC.
  %hop1
  0.7::factX:-xor(factA,factB).
  0.9::factY:-and(factB,factA).
  0.8::factZ:-and(factA,factB).

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

  query(conclusion).
  
'Mary left the apple' or 'Julius is a lion' or both.