## Laws of correction

McKean's Law

Any correction of the speech or writing of others will contain at least one grammatical, spelling, or typographical error.
Skitt's Law
Any post correcting an error in another post will contain at least one error itself.
Muphry's Law
If you write anything criticizing editing or proofreading, there will be a fault of some kind in what you have written.
Hartman's Law of Prescriptivist Retaliation
Any article or statement about correct grammar, punctuation, or spelling is bound to contain at least one eror.

## UID numbering scheme

Some thoughts on A UID numbering scheme - A paper published by Unique Identification Authority of India.

1. Process for De-duplication (page 5)
Since biometric information contain no ordering and hence cannot be indexed like text based information, when a resident applies for a UID with his/her fingerprints, iris and photo of face, these biometrics have to be compared against the entire UID database (existing residents with UIDs) to ensure that this new applicant is indeed unique and has not already been allotted a UID (even under a different name, address etc). This 1:N biometric comparison (N=size of the UID database) is the most compute intensive operation of the UID server systeem.
It sounds as if the search operation would take O(N) time. Why can't the data be treated as binary numbers that can be ordered and indexed? It'll improve the search time to at least O(log N) and possibly even more if good algorithms are used. The difference is huge when N is as large as 1.2 billion.
2. Memorization of UID (page 6)
This section is about how long the string length should be. In short, the string has to be as short as possible but that meets density requirement and does not include alphabet characters, just numbers. It is important to keep the UID simple and small to help residents to remember their number.
Firstly the use of the hindu-arabic numeral system(0,1,2,3,4,5,6,7,8,9) is suggested since these numerals are recognized/used by the largest subset of people in the country. Secondly we suggest the use of 12 digits (11 + 1 check sum) since 11 digits gives us a 100billion number space which in turn can provide a low density of used numbers.
A 12 digit UID doesn't sound like an easy thing to memorize. However, this length is necessary to ensure 80 billion unique UIDs.
3. UID static PIN and dynamic PIN (page 7)
In order to authenticate(ascertain it is who s/he claims to be) a resident needs to provide his/her UID number as well as say a biometric marker – such as a fingerprint.
Using biometrics while issuing UIDs may be fine. But using biometrics for other important transactions might put the user at risk. e.g. Malaysia car thieves steal finger
4. Principles and Requirements (page 11)
Number Generation: The numbers are generated in a random, non-repeating sequence. There are several approaches to doing this in the computer science literature. The algorithm and any"seed" chosen to generate IDs should not be made public and should be considered a national secret.
This violates Shannon's maxim, "The enemy knows the system". Why can't the system rely on the secrecy of the seed only?
5. The Checksum (page 12)
There is one scheme that meets our requirements: the Verhoeff Scheme. This scheme is relatively complex, and in the days before ubiquitous computing, there was a tendency to avoid it in favor of simpler schemes. In this day and age however, and at the scale of the UID, precision must be the goal. The Verhoeff scheme catches all single errors and all adjacent transpositions. It also catches >95% of twin errors and >94% of jump transpositions.
More information on the scheme can be found here: http://www.cs.utsa.edu/~wagner/laws/verhoeff.html and http://en.wikipedia.org/wiki/Verhoeff_algorithm.
Update: I mailed this link to Nandan Nilekani and he responded by requesting me to send this as a document to him which I eventually did.

## Verifying the π recitation by booksonmyhead

Tried verifying the π recitation in the following video (balancing 15 books on my head, reciting pi to the 100th digit, and solving a rubik's cube.) by :

The first row has the first 100 digits of π. The second row has the digits I think she recited. The third row has markers for my comments.

3.14159 265358 979323 8462643 38327 9502884 1971 693993 75105
3.14159 265358 979323 8462643 383*7 9502884 1971 693993 75105
'''*

8209749 445923 07816 4062862 08998 628 03482534 2117067
8209749 445923 07816 4062862 08998 628 03482534 2117067
^^                               ~~

''' - She said, "three eight three", very quickly. I could hear the 'eight' clearly only after playing the video at a speed of 0.63x

* - I'm not sure if she really said, "two", there. It sounds more like 'point' even at 0.63x.

^^ - She says, "sixteen", there. It wasn't clear to me first. Had to listen it for the second time to be sure.

~~ - It sounds like she missed the 'zero'. However, on listening carefully at 0.63x speed, I feel she probably said 'O' quickly after saying, "seven".