Periodic charge sequence centered

Definition 1.9 covers directly the case of copolymers and without loss of generality it is natural to assume that a periodic copolymer is a copolymer with a centered periodic charge sequence. Note that in this case if /t > 0, by restricting the attention only to S trajectories that are positive in 1,..., nT - 1, we have... 

Definition 1.9 A charge sequence u>n n is weakly inhomogeneous or periodic if there exists T G N such that u n+r = for every n. The minimal such T is called the period and it is denoted by T(w). A periodic sequence is said centered if = 0. 

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