Comment: Scarce vs. Rivalrousness

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Scarce vs. Rivalrousness

Is one's labor scarce? Is it rivalrous? Is one's mental labor rivalrous? Can someone inhabit my brain and use it while I am using it to create an idea of some kind?

I'm not being facetious, I am still weighing all sides of this issue, but these are the kinds of thoughts that pop into my head when discussing scarcity vs. rivarlousness.
*Advancing the Ideas of Liberty Daily*