parcau. The trimmed L-moments in terms of the parameters are $\lambda^{(1)}_1 = \xi$,
$\lambda^{(1)}_2 = 0.698\alpha$, $\tau^{(1)}_3 = 0$, and $\tau^{(1)}_4 = 0.343$. These TL-moments (trim=1) are symmetrical for the first L-moments defined because $\mathrm{E}[X_{1:n}]$ and $\mathrm{E}[X_{n:n}]$ undefined expectations for the Cauchy.
lmomcau(para)list is returned.Elamir, E.A.H., and Seheult, A.H., 2003, Trimmed L-moments: Computational Statistics and Data Analysis, v. 43, pp. 299--314.
parcau, cdfcau, pdfcau, quacau X1 <- rcauchy(20)
lmomcau(parcau(TLmoms(X1,trim=1)))
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