It is probably the case that Brian is a frog. There is almost no chance that Fred is in the school. It is probably not the case that Bernhard is yellow. Chances are about even that if either 'Bernhard is yellow' or 'Brian is a frog' but not both then Julius is a rhino. It is impossible that if 'Fred is in the school and Bernhard is yellow' then Gertrude is a mouse. We doubt that if 'Brian is a frog and Fred is in the school' then Bill left the football.
There is almost no chance that 'Fred is in the school' or 'Gertrude is a mouse' or both.
There is almost no chance that 'Fred is in the school' or 'Gertrude is a mouse' or both.
It is almost certain that 'Fred is in the school' or 'Gertrude is a mouse' 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
  0.7::factA.
  0.02::factB.
  0.25::factC.
  %hop1
  0.5::factX:-xor(factC,factA).
  0.0::factY:-and(factB,factC).
  0.2::factZ:-and(factA,factB).

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

  query(conclusion).
  
'Fred is in the school' or 'Gertrude is a mouse' or both.