We believe that Greg is a swan. It is impossible that Emily is a mouse. It is probably the case that Mary dropped the milk. It is likely that if either 'Mary dropped the milk' or 'Greg is a swan' but not both then Fred left the football. Chances are about even that if 'Mary dropped the milk and Greg is a swan' then Bernhard is a swan. There is little chance that if 'Mary dropped the milk' or 'Emily is a mouse' or both then John moved to the garden.
It is highly unlikely that 'John moved to the garden and Mary dropped the milk'.
It is highly unlikely that 'John moved to the garden and Mary dropped the milk'.
We believe that 'John moved to the garden and Mary dropped the milk'.

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

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

  query(conclusion).
  
'John moved to the garden and Mary dropped the milk'.