Date of Original Version
This is a contribution to the partial basis problem and, in particular, to the case where the basis elements are cosigns or consecutive powers cosines. We contribute also to the general theory of Tchebycheff systems to which the partial basis problem is strongly related.
Shisha, O. (1980). Tchebycheff systems and best partial bases. Pacific Journal of Mathematics, 86(2), 579-592. doi: 10.2140/pjm.1980.86.579
Available at: http://dx.doi.org/10.2140/pjm.1980.86.579