We believe that Julius is a lion. We believe that Brian is white. It is probably the case that Greg is yellow. There is little chance that if 'Greg is yellow and Julius is a lion' then Bernhard is a rhino. It is highly unlikely that if 'Greg is yellow' or 'Brian is white' or both then Mary dropped the milk. There is a very good chance that if 'Julius is a lion' or 'Greg is yellow' or both then Fred left the football.
It is improbable that 'Fred left the football' or 'Greg is yellow' or both.
It is highly likely that 'Fred left the football' or 'Greg is yellow' or both.
It is improbable that 'Fred left the football' or 'Greg is yellow' 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
  0.75::factA.
  0.75::factB.
  0.7::factC.
  %hop1
  0.1::factX:-and(factC,factA).
  0.05::factY:-or(factC,factB).
  0.8::factZ:-or(factA,factC).

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

  query(conclusion).
  
'Fred left the football' or 'Greg is yellow' or both.