There is a continuing interplay between mathematics and survey methodology
involving different branches of mathematics, not only probability. This interplay is
quite obvious as regards the first of the two options: probability vs. non-probability
sampling, as proposed and discussed in Kalton (2023). There, mathematics is represented
by probability and mathematical statistics. However, sometimes connections between
mathematics and survey methodology are less obvious, yet still crucial and intriguing.
In this paper we refer to such an unexpected relation, namely between rotation sampling
and Chebyshev polynomials. This connection, introduced in Kowalski and Wesołowski
(2015), proved fundamental for the derivation of an explicit form of the recursion for
the BLUE µˆt of the mean on each occasion t in repeated surveys based on a cascade
rotation scheme. This general result was obtained under two basic assumptions:
ASSUMPTION I and ASSUMPTION II, expressed in terms of the Chebyshev polynomials.
Moreover, in that paper, it was conjectured that these two assumptions are always
satisfied, so the derived form of recursion is universally valid. In this paper, we
partially confirm this conjecture by showing that ASSUMPTION I is satisfied for rotation
patterns with a single gap of an arbitrary size.