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   Three-dimensional rotations can be represented by three real numbers
   (Euler angles), four real numbers (unit quaternions) or nine real numbers
   (orthogonal matrices with determinant 1).   Quaternions, at the price of
   carrying one more number than necessary, are supremely elegant and
   have certain practical advantages too.

   This module provides an extended idiomatic Lua interface to the CQRlib
   library written by Herbert J. Bernstein. It is not a "binding"; access to
   the original documentation is only required for those who wish to
   understand the module's C code lcqr.c.

   A quaternion is implemented as an immutable userdata consisting of
   four double precision numbers. The metatable of that module, which is
   its own __index, is returned by require "cqr".

   Liberal use is made of the additional binary operators of Lua 5.3, e.g.
      a // (p|q)
   means "a rotated by the quaternion that rotates p to lie on q".

   The C code, as well as a test suite in Lua and HTML documentation and
   a Makefile for Linux, can be found at

   -- Dirk