MIT License

About JavaScript etc. code in this eBook (under MIT Licensed
  exept content text.)                                                          
                                                                                     
Copyright (c) 2021 - people tree publishing (Hirosato Matsuura)
                       - https://digipub.me                 
                                     
Permission is hereby granted, free of charge, to any person
obtaining a copy of this software and associated documentation                  
files (the "Software"), to deal in the Software without restriction,            
 including without limitation the rights to use, copy, modify,                  
merge, publish, distribute, sublicense, and/or sell copies of                   
the Software, and to permit persons to whom the Software is                     
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The above copyright notice and this permission notice shall                     
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NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT                     
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER                   
DEALINGS IN THE SOFTWARE.