Abstract(#br)We prove a comprehensive solution theory using tools from functional analysis, show corresponding variational formulations, and present functional a posteriori error estimates for general linear first order systems of type
for two densely defined and closed (possibly unbounded) linear operators A1 and A2 having the complex property . As a prototypical application we will discuss the system of electro-magneto statics in 3D with mixed tangential and normal boundary conditions
... position="float" orientation="portrait" xlink:href="lnfa_a_1490756_m0002.gif"/> Our theory covers a lot more applications in 2D, 3D, and ND, such as general differential forms and all kind of systems arising, e.g., in general relativity, biharmonic problems, Stokes equations, or linear elasticity, to mention just a few, for example
all with possibly mixed boundary conditions of generalized tangential and normal type. Second order systems of types
will be considered as well using the same techniques.