Revert "Added a definition of gCn and embedded YT video."

This reverts commit eb02f5b182a44d9aa0dad8b7b5c1721642e129fd.
Revert "Revert "Added a definition of gCn and embedded YT video.""

This reverts commit f8e826a2e2e2bb2c347e64dfe17f1bffe8196c36.