> for example, it is very natural to name them "a,A,b,B"

And just to clarify once again, since I'm not sure who will read which reply: those are NOT the same identifiers in Nim!

    let
      a = 11
      b = 22
      A = 99
      B = 88

    echo a == A # false
    echo b == B # false

Run the code in the Nim Playground if you don't believe: https://play.nim-lang.org/#ix=20kr