  Aims: The hard and soft spectral states of black hole accretion are
understood as connected with ADAF accretion (truncated disk) and standard disk
accretion, respectively. However, observations indicate the existence of cool
gas in the inner region at times when the disk is already truncated outside. We
try to shed light on these not yet understood intermediate states. Methods: The
disk-corona model allows to understand the spectral state transitions as caused
by changes of the mass flow rate in the disk and provides a picture for the
accretion geometry when disk truncation starts at the time of the soft/hard
transition, the formation of a gap in the disk filled by an advection-dominated
flow (ADAF) at the distance where the evaporation is maximal. We study the
interaction of such an ADAF with an inner thin disk below. Results: We show
that, when the accretion rate is not far below the transition rate, an inner
disk could exist below an ADAF, leading to an intermediate state of black hole
accretion.
