The line blurs for sure. I would say it's 'a' kernel. The idea of there only being one kernel is probably a concept that makes for nice layered diagrams, but

The line blurs for sure. I would say it's 'a' kernel. The idea of there only being one kernel is probably a concept that makes for nice layered diagrams, but doesn't come close to describing reality because of the combinatorial complexity of options for different morphs of layering. Sort of like the OSI network layers model in that way.