It is not clear if the software is licensed by either MIT or Happy Bunny or BOTH by MIT and Happy Bunny.
In the official website ( https://glm.g-truc.net/0.9.9/index.html ) I notice "OR":
"The source code and the documentation, including this manual, are licensed under the Happy Bunny License (Modified MIT) or the MIT License."
Also, there is "OR" in the readme.md ( https://github.com/g-truc/glm )
"The source code and the documentation are licensed under both the Happy Bunny License (Modified MIT) or the MIT License."
This helps GLM fit into build systems which expect the license to be
contained in a single distinct file.
The file was downloaded from https://glm.g-truc.net/copying.txt