Benchmark "rz-kerb" : Poisson problem with re-entrant corner, rotational symmetric domain (Poisson-Problem mit einspringender Ecke , rotationssymmetrisch)

Material coefficients:	a1	a2	c
	1.	1.	0.
source term :	f
	0.
Boundary conditions :
Dirichlet - type:	u=0	at z=0
Neumann - type:	du/dn=1	at z=1

Typical behavior of estimated relative error:
(Das typische Verhalten des geschaetzten rel. Fehlers) (Legend)

here some RUNs with times / iteration numbers / etc.