Question: How to check if a name not in initially known names?

I think I remeber doing this before but not sure and it is not in my cheat sheet.

Given an expression, I wanted to find all names in it. Which can be done using indets(f,name);

But then how to check if any of the names found are not in the Maple initial known names given in https://www.maplesoft.com/support/help/Maple/view.aspx?path=initialconstants

For example,

f:=x^2 - y^2+Pi;
indets(f,name);

Gives {Pi, x, y}  how does one then check if this list does not have any known name in it?

In this case Pi. I do not want to check explicitly for each name listed on the web page above.

Are these initial known names  grouped in some specific maple type that can be used to check against?

Or is there a command in Maple to return a list of all these initially known names? If so this list can be used to check against.

Asked google AI and it did not know.

Maple 2025.2