Well those constraints simplify your problem.

In the resultant dataset, the largest X and Y values will be equal, and the 
largest X will have and entry for every coordinate from (X, 1) to (X, X). 
Likewise the largest Y will have an entry for every coordinate from (1, Y) to 
(Y, Y). Basically you'll have two lines from the axes, drawing a square. All 
points outside that square will be culled, all points on and inside the square 
will be kept.

Since you know that, you now have a one dimensional problem to solve. It still 
seems a little recursive to me, but it should be easier because you only need 
to find a single number (which you can then plug into a delete statement).

If my statement about the square is not obvious to prove in your head I can try 
write a proof for that but I'm not much good at proofs.

> On 2 May 2018, at 7:27 am, Roman Fleysher <roman.fleys...@einstein.yu.edu> 
> wrote:
> 
> Pairs (x,y) do not repeat.
> 
> Actual x and y are positive integers, but I do not see how being positive can 
> be relevant. Integer is important for sorting/comparison.
> 
> 
> Roman
> 
> ________________________________________
> From: sqlite-users [sqlite-users-boun...@mailinglists.sqlite.org] on behalf 
> of Barry Smith [smith.bar...@gmail.com]
> Sent: Tuesday, May 01, 2018 5:23 PM
> To: SQLite mailing list
> Subject: Re: [sqlite] probably recursive?
> 
> Is there a uniqueness constraint on your initial data? Can the same 
> coordinate be listed multiple times?
> 
> Is there a requirement that X > 0 and Y > 0?
> 
>>> On 2 May 2018, at 3:35 am, Simon Slavin <slav...@bigfraud.org> wrote:
>>> 
>>> On 1 May 2018, at 6:28pm, Simon Slavin <slav...@bigfraud.org> wrote:
>>> 
>>> I just realised that
>> 
>> That was intended to be personal email.  Apologies, everyone.
>> 
>> Simon.
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