It is highly unlikely that Mary went to the kitchen. It is probably the case that Fred is in the school. There is almost no chance that Jessica is a cat. It is unlikely that if 'Mary went to the kitchen and Fred is in the school' then Gertrude is a sheep. It is probably not the case that if 'Jessica is a cat' or 'Mary went to the kitchen' or both then Lily is a lion. Chances are about even that if 'Mary went to the kitchen' or 'Jessica is a cat' or both then Sandra left the football.
It is highly unlikely that 'Mary went to the kitchen' or 'Gertrude is a sheep' or both.
It is highly unlikely that 'Mary went to the kitchen' or 'Gertrude is a sheep' or both.
There is a very good chance that 'Mary went to the kitchen' or 'Gertrude is a sheep' 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.
  0.7::factB.
  0.02::factC.
  %hop1
  0.2::factX:-and(factA,factB).
  0.25::factY:-or(factC,factA).
  0.5::factZ:-or(factA,factC).

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

  query(conclusion).
  
'Mary went to the kitchen' or 'Gertrude is a sheep' or both.