# A confusion about linear span of modified de Bruijn sequence

Recently i'm reading "Cryptographically Strong de Bruijn Sequences with Large Periods" . In the section 2 2.1 Basic Denitions and Properties , property 1 says that $$2n<LS_s\leq2^n-2$$ The author claims that this bound comes from "Characterizations of Generators for Modified de Bruijn Sequences". I go through it, but i never find this bound in it.

I wonder how this bound comes? Can someone prove it? Or does someone know some related paper about it? thanks ..

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