# Closed natural numbers

I am reading this paper about interleavers for turbo code design, and when it describes the so called block interleavers, it says that

To obtain a block interleaver function it is necessary to factorize its length:

$$N_b=X\times Y$$

where $$X$$ and $$Y$$ are closed natural numbers.

I have been looking around what the word closed means for natural numbers, but I have only found definitions about closure of sets, and not individual numbers. I am wondering what could such thing mean in this context.

• (+1) I have no idea either what could be meant. Maybe just a mistake ? – Peter Jan 28 at 12:02
• The authors are Romanian. Perhaps a mistranslation ("false friend") – Hagen von Eitzen Jan 28 at 12:31

## 1 Answer

After researching more about the topic, I found out the PhD thesis of KOVACI, which is one of the authors of the paper I cited. Such disertation is written in Romanian, and I am pretty sure that the suggestion by Hagen von Eitzen is indeed what happened here. After translating the original text in Romanian with Google traductor (not sure if it is the best option, but it is the only one I have), I found out that what they might be stating is not that $$X$$ and $$Y$$ should be closed natural numbers, but natural numbers that are close. That intuition seems to be good as the numbers they select for their simulations for the block interleaver are indeed close natural numbers such as $$X=29$$ and $$Y=31$$.