Chances are slight that Mary went to the hallway. Chances are about even that John took the apple. It is probably the case that Greg is green. Chances are slight that if 'Greg is green' or 'John took the apple' or both then Brian is a swan. It is improbable that if 'Mary went to the hallway and Greg is green' then Sandra left the football. There is a better than even chance that if 'Mary went to the hallway and Greg is green' then Lily is a frog.
We believe that 'Brian is a swan and John took the apple'.
It is highly unlikely that 'Brian is a swan and John took the apple'.
We believe that 'Brian is a swan and John took the apple'.

  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
  0.1::factA.
  0.5::factB.
  0.7::factC.
  %hop1
  0.1::factX:-or(factC,factB).
  0.1::factY:-and(factA,factC).
  0.6::factZ:-and(factA,factC).

  %hop2
  conclusion:-and(factX,factB).

  query(conclusion).
  
'Brian is a swan and John took the apple'.