Have not checked this forum for quite some time. It appears I should. I really like the tones you have managed to get out of a paper negative Reinhold. I bought some 4X5 VC paper from Ultrafine but even with preflashing cannot control the contrast. Very hard to get a range of grays. I've had some success with Ilford MGIV, it seems work much better than the Ultrafine brand.
Addressing tkamiya's question;
It is much easier to do than to get your head around it.
Really it is the same as any negative/positive process. You are just replacing the film with photo paper. That gives you a negative that is reversed from left to right (a mirror image if you will). Then just lay that negative, emulsion to emulsion on photo paper, place a heavy piece of clean glass on top to keep then in contact, and expose with white light for a few seconds. Process the bottom paper as you would any darkroom print and you will wind up with a positive with the correct orientation.
The difference between a paper negative and a film negative is that the film negative is on a transparent base so that it can be viewed from either side. A paper negative base is, well it's paper, so can only be seen clearly from the front (emulsion side). The making of a print from a negative is the same principal. When you stick the negative in the enlarger the emulsion still has to face the paper.
I must now muddy the waters a bit. Just a small exception. A negative from a Tessina has to be printed emulsion up. That is because the image from the lens is bounced 90 degrees from a first surface mirror onto the film and thus, when viewed from the emulsion side is not reversed, left to right.