An interval also includes the upperbound

[wmo]

First of all, thanks for making your notes available.

There is a minor correction I want to make regarding:
https://docs.plutus-community.com/docs/lectures/Lecture3.html

It says: @interval a b@ includes all values that are greater than or equal to @A@ and smaller than @b@. Therefore it includes @A@ but it does not include @b@.

That is wrong, because upperbound b is also included. Try it in the REPL.

let iv = interval (10 :: Integer) 20
member 10 iv    GIVES   True
member 20 iv    GIVES   True
member 21 iv    GIVES   False

If you look at lines 203-206 of source code plutus-ledger-api/src/Plutus/V1/Ledger/Interval.hs
-- | @interval a b@ includes all values that are greater than or equal to @A@
-- and smaller than or equal to @b@. Therefore it includes @A@ and @b@.

(all this may be due to a plutus source code change?)