  An initial boundary value problem of the nonlinear diffusion equation with a
dynamic boundary condition is treated. The existence problem of the
initial-boundary value problem is discussed. The main idea of the proof is an
abstract approach from the evolution equation governed by the subdifferential.
To apply this, the setting of suitable function spaces, more precisely the
mean-zero function spaces, is important. In the case of a dynamic boundary
condition, the total mass, which is the sum of volumes in the bulk and on the
boundary, is a point of emphasis. The existence of a weak solution is proved on
this basis.
