RFC on range design for D2

[Manfred_Nowak]

Dejan Lekic wrote:

> r.fromBegin(s) is really s.toEnd(r)

Might be true only, if `s' equals `r'.

Otherwise at least one seems to be undefined, because not both can be 
true subranges of each other. 

I used the conjunctive form, because a formal definition of "subrange" 
is missing. Such is needed because in a cyclic model `s' and `r' might 
be equal, but not identical, because they contain a whole cycle, but 
their start points differ.

-manfred

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