Question: calculating with lists

i have a list of numeric values like this:

r:=[a,b,c,....]

now i want to calculate the quantity

s:=lambda-r^2

which in turn should give me a list again whose entries are:

[lambda-a^2,lambda-b^2,...]

but just doing

s:=lambda-r^2 doesnt work.

lambda is an arbitrary number

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