  The threshold behaviour of the K-Satisfiability problem is studied in the
framework of the statistical mechanics of random diluted systems. We find that
at the transition the entropy is finite and hence that the transition itself is
due to the abrupt appearance of logical contradictions in all solutions and not
to the progressive decreasing of the number of these solutions down to zero. A
physical interpretation is given for the different cases $K=1$, $K=2$ and $K
\geq 3$.
