Regular black holes and energy conditions
  We establish the relationship between the space-time structure of regular
spherically-symmetrical black holes and the character of violation of the
strong energy condition (SEC). It is shown that it is violated in any static
region under the event horizon in such a way that the Tolman mass is negative
there. In non-static regions there is constraint of another kind which, for a
perfect fluid, entails violation of the dominant energy condition.
