There is almost no chance that Fred is in the school. It is improbable that Julius is yellow. Chances are about even that Greg is a frog. It is improbable that if 'Greg is a frog and Fred is in the school' then Mary took the football. It is probably the case that if 'Greg is a frog and Julius is yellow' then Sandra dropped the apple. There is a very good chance that if 'Greg is a frog and Julius is yellow' then Daniel left the milk.
It is highly unlikely that 'Fred is in the school' or 'Daniel left the milk' or both.
It is highly unlikely that 'Fred is in the school' or 'Daniel left the milk' or both.
It is probable that 'Fred is in the school' or 'Daniel left the milk' 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
  0.02::factA.
  0.1::factB.
  0.5::factC.
  %hop1
  0.1::factX:-and(factC,factA).
  0.7::factY:-and(factC,factB).
  0.8::factZ:-and(factC,factB).

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

  query(conclusion).
  
'Fred is in the school' or 'Daniel left the milk' or both.