Stop speaking for us. Personally, I saw that you got confused between your own ideas. In deflation (or whatever) no one will charge negative interest rate for loans, whether real or nominal. You may build any theories, but this simple fact will leave no stone of them in practice.
When I use "we" I mean often "I".
I'm terribly sorry that the mathematics was beyond you
The negative nominal interest resulted from YOUR artificially demanded example.
The very first example I gave was perfectly OK. Then you insisted on me applying the same rules to examples of which YOU specified the (impossible) conditions.
That was to show the absurdity of your ideas (i.e. deflation being the mirror of inflation).
Of course nominal interest cannot get negative. It won't. That doesn't mean that the real interest doesn't exist, and that there is no compensation for deflation or inflation.
It just means that in deflation debt will most likely be more burdensome (the higher the deflation), since nominal interest rate will always be over 0 (whatever deflation rates might be). You are still arguing your primarily point?