Hello,
I implemented it now as follows which seems to be working and still keeps the code compact:
M = L2(mesh, order = order)
X = FESpace([M, M, M, M])
L11, L12, L21, L22 = X.TrialFunction()
L = CoefficientFunction(( (L11, L12), (L21, L22) ))
LT = CoefficientFunction(( (L11, L21), (L12, L22) ))
Thanks,
Sander