Here, glslang proper means core GLSL parsing, HLSL parsing, and SPIR-V code
generation. Glslang proper requires use of a number of licenses, one that covers
preprocessing and others that covers non-preprocessing.

Bison was removed long ago. You can build glslang from the source grammar,
using tools of your choice, without using bison or any bison files.

Other parts, outside of glslang proper, include:

- gl_types.h, only needed for OpenGL-like reflection, and can be left out of
  a parse and codegen project.  See it for its license.

- update_glslang_sources.py, which is not part of the project proper and does
  not need to be used.

- the SPIR-V "remapper", which is optional, but has the same license as
  glslang proper

- Google tests and SPIR-V tools, and anything in the external subdirectory
  are external and optional; see them for their respective licenses.

--------------------------------------------------------------------------------

The core of glslang-proper, minus the preprocessor is licenced as follows:

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   Bison implementation for Yacc-like parsers in C

   Copyright (C) 1984, 1989-1990, 2000-2015 Free Software Foundation, Inc.

   This program is free software: you can redistribute it and/or modify
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--------------------------------------------------------------------------------
================================================================================
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The preprocessor has the core licenses stated above, plus an additional licence:

/****************************************************************************\
Copyright (c) 2002, NVIDIA Corporation.

NVIDIA Corporation("NVIDIA") supplies this software to you in
consideration of your agreement to the following terms, and your use,
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software.

In consideration of your agreement to abide by the following terms, and
subject to these terms, NVIDIA grants you a personal, non-exclusive
license, under NVIDIA's copyrights in this original NVIDIA software (the
"NVIDIA Software"), to use, reproduce, modify and redistribute the
NVIDIA Software, with or without modifications, in source and/or binary
forms; provided that if you redistribute the NVIDIA Software, you must
retain the copyright notice of NVIDIA, this notice and the following
text and disclaimers in all such redistributions of the NVIDIA Software.
Neither the name, trademarks, service marks nor logos of NVIDIA
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NVIDIA Software without specific prior written permission from NVIDIA.
Except as expressly stated in this notice, no other rights or licenses
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THE NVIDIA SOFTWARE IS BEING PROVIDED ON AN "AS IS" BASIS, WITHOUT
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ITS USE AND OPERATION EITHER ALONE OR IN COMBINATION WITH OTHER
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IN NO EVENT SHALL NVIDIA BE LIABLE FOR ANY SPECIAL, INDIRECT,
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