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Let q be a power of a prime and F q be a finite field with q elements. In this paper, we propose four families of infinite classes of permutation trinomials having the form cx − x s + x qs over F q 2 , and investigate the relationship between this type of permutation polynomials with that of the form (x q − x + δ) s + cx. Based on this relation, many classes of permutation trinomials having the form (x q − x + δ) s + cx without restriction on δ over F q 2 are derived from known permutation trinomials having the form cx − x s + x qs .

In distributed storage systems, locally repairable codes (LRCs) are designed to reduce disk I/O and repair costs by enabling recovery of each code symbol from a small number of other symbols. To handle multiple node failures, (r, δ)-LRCs are introduced to enable local recovery in the event of up to δ −1 failed nodes. Constructing optimal (r, δ)-LRCs has been a significant research topic over the past decade. In [24], Luo et al. proposed a construction of linear codes by using unions of some projective subspaces within a projective space. Several new classes of Griesmer codes and distance-optimal codes were constructed, and some of them were proved to be alphabet-optimal 2-LRCs.In this paper, we first modify the method of constructing linear codes in [24] by considering a more general situation of intersecting projective subspaces. This modification enables us to construct good codes with more flexible parameters. Additionally, we present the conditions for the constructed linear codes to qualify as Griesmer codes or achieve distance optimality. Next, we explore the locality of linear codes constructed by eliminating elements from a complete projective space. The novelty of our work lies in establishing the locality as (2, p − 2), (2, p − 1), or (2, p)-locality, in contrast to the previous literature that only considered 2-locality. Moreover, by combining analysis of code parameters and the C-M like bound for (r, δ)-LRCs, we construct some alphabet-optimal (2, δ)-LRCs which may be either Griesmer codes or not Griesmer codes. Finally, we investigate the availability and alphabet-optimality of (r, δ)-LRCs constructed from our modified framework.