There is a very good chance that Greg is a lion. We doubt that John picked up the apple. It is likely that Brian is a swan. Chances are about even that if 'John picked up the apple and Brian is a swan' then Yann is hungry. There is little chance that if 'Brian is a swan' or 'Greg is a lion' or both then Mary went to the office. It is improbable that if 'Brian is a swan' or 'Greg is a lion' or both then Sandra took the milk.
Chances are about even that 'Yann is hungry and Greg is a lion'.
It is highly unlikely that 'Yann is hungry and Greg is a lion'.
Chances are about even that 'Yann is hungry and Greg is a lion'.

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

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

  query(conclusion).
  
'Yann is hungry and Greg is a lion'.