It is probably the case that John picked up the apple. There is little chance that Mary went to the kitchen. It is probably not the case that Greg is white. There is a better than even chance that if 'Greg is white' or 'John picked up the apple' or both then Sandra dropped the milk. It is highly likely that if 'Mary went to the kitchen and John picked up the apple' then Lily is yellow. Chances are slight that if 'Greg is white and Mary went to the kitchen' then Jason is tired.
It is probably not the case that 'Greg is white' or 'Lily is yellow' or both.
It is probably not the case that 'Greg is white' or 'Lily is yellow' or both.
There is a very good chance that 'Greg is white' or 'Lily 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
  0.7::factA.
  0.1::factB.
  0.25::factC.
  %hop1
  0.6::factX:-or(factC,factA).
  0.9::factY:-and(factB,factA).
  0.1::factZ:-and(factC,factB).

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

  query(conclusion).
  
'Greg is white' or 'Lily is yellow' or both.