Question: how to obtain list of protected names in Maple?

Is there a command or method in Maple to list all initially protected names?

This page list undocumented protected names, and this page  lists initially known names, which I assume are all protected.

But what about a list of all protected names? sin,cos, eval, uneval, etc.. any name that can't be assigned to. In my search so far, I could not find how to find these names. There are 100's of such names. Can one get them all in a list to look at?

Using Maple 2019.1

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