We believe that Greg is gray. It is impossible that Bernhard is a frog. There is a better than even chance that Julius is white. There is little chance that if 'Greg is gray' or 'Julius is white' or both then Fred left the football. It is highly unlikely that if either 'Julius is white' or 'Bernhard is a frog' but not both then Lily is green. It is highly unlikely that if 'Bernhard is a frog and Greg is gray' then Mary picked up the apple.
It is impossible that 'Mary picked up the apple and Greg is gray'.
It is impossible that 'Mary picked up the apple and Greg is gray'.
It is likely that 'Mary picked up the apple and Greg is gray'.

  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.
  0.0::factB.
  0.6::factC.
  %hop1
  0.1::factX:-or(factA,factC).
  0.05::factY:-xor(factC,factB).
  0.05::factZ:-and(factB,factA).

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

  query(conclusion).
  
'Mary picked up the apple and Greg is gray'.