How to use the same variable names for input and output
There is the question in the light of !1039 (merged) how to use the same names for primary variables for input and output. Until now !1039 (merged) specifies the privar names for input but doesn't influence the ones for output. Option 1 is that this is wanted -> I want to be able to read any file and just supply the field names myself. Option 2 is that we somehow force the same names for the output (which might be complicated because output doesn't care about which variables are privars right now).