We construct the systems of bi-orthogonal polynomials on the unit circle where the Toeplitz structure of the moment determinants is replaced by $$\det (w_{2j-k})_{0\le j,k \le N-1} $$
det
(
w
2
j
-
k
)
0
≤
j
,
k
≤
N
-
1
and the corresponding Vandermonde modulus squared is replaced by $$\prod _{1 \le j < k \le N}(\zeta _k - \zeta _j)(\zeta ^{-2}_k - \zeta ^{-2}_j) $$
∏
1
≤
j
<
k
≤
N
(
ζ
k
-
ζ
j
)
(
ζ
k
-
2
-
ζ
j
-
2
)
. This is the simplest case of a general system of $$pj-qk$$
p
j
-
q
k
with p, q co-prime integers. We derive analogues of the structures well known in the Toeplitz case: third order recurrence relations, determinantal and multiple-integral representations, their reproducing kernel and Christoffel–Darboux sum, and associated (Carathéodory) functions. We close by giving full explicit details for the system defined by the simple weight $$ w(\zeta )=e^{\zeta }$$
w
(
ζ
)
=
e
ζ
, which is a specialisation of a weight arising from averages of moments of derivatives of characteristic polynomials over $$\textrm{USp}(2N)$$
USp
(
2
N
)
, $$\textrm{SO}(2N)$$
SO
(
2
N
)
and $$\textrm{O}^-(2N)$$
O
-
(
2
N
)
.