General Riemann-Liouville linear two-point boundary value problems of order αp, where n − 1 < αp < n for some positive integer n, are investigated on the interval [0,b]. It is shown first that the natural degree of regularity to impose on the solution y of the problem is y∈Cn−2[0,b]\documentclass[12pt]{minimal}
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\begin{document}$y\in C^{n-2}[0,b]$\end{document} and Dαp−1y∈C[0,b]\documentclass[12pt]{minimal}
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\begin{document}$D^{\alpha _{p}-1}y\in C[0,b]$\end{document}, with further restrictions on the behavior of the derivatives of y(n− 2) (these regularity conditions differ significantly from the natural regularity conditions in the corresponding Caputo problem). From this regularity, it is deduced that the most general choice of boundary conditions possible is y(0)=y′(0)=…=y(n−2)(0)=0\documentclass[12pt]{minimal}
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\begin{document}$y(0) = y^{\prime }(0) = {\dots } = y^{(n-2)}(0) = 0$\end{document} and ∑j=0n1βjy(j)(b1)=γ\documentclass[12pt]{minimal}
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\begin{document}${\sum }_{j = 0}^{n_{1}}\beta _{j}y^{(j)}(b_{1}) =\gamma $\end{document} for some constants βj and γ, with b1 ∈ (0,b] and n1∈{0,1,…,n−1}\documentclass[12pt]{minimal}
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\begin{document}$n_{1}\in \{0, 1, \dots , n-1\}$\end{document}. A wide class of transformations of the problem into weakly singular Volterra integral equations (VIEs) is then investigated; the aim is to choose the transformation that will yield the most accurate results when the VIE is solved using a collocation method with piecewise polynomials. Error estimates are derived for this method and for its iterated variant. Numerical results are given to support the theoretical conclusions.
