In 1985 Halperin authored a text on grading coins, How to Grade U.S. Coins, upon which the grading standards of the two leading third-party grading services PCGS and NGC were ultimately based.
Parallel communicating grammar systems, grammar systems working on their own string and communicating with other grammars in a system by sending their sequential forms on request.
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Professional Coin Grading Service, an authentication and grading service for rare coins started by seven coin dealers in 1985 to standardize coin grading.
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Preconditioned conjugate gradient square method, a variant of the preconditioned conjugate gradient method - an algorithm for the numerical solution of systems of linear equations whose matrix is symmetric and positive-definite.
In the May 26, 2003 edition of Coin World, the hobby newspaper had announced they had contracted investigators to conduct a year-long, comparative study of PCGS, ACCGS, NGC (Numismatic Guaranty Corporation) and several other grading services, each known as a Third Party Grader (TPG).
It is used by nearly all major coin grading companies, the main two being NGC and PCGS.
The influence of the book has caused the incorrect spelling "piefort" to be used by third-party grading services such as NGC and PCGS in labeling coin attributions.
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