In this paper, we present a direct construction and a recursive construction of the affine-invariant 2-fold quadruple systems of order q (3-(q, 4, 2) designs), where q is a prime power. The direct construction also gives a criterion for the existence of affine-invariant 2-fold quadruple systems of prime order by using 1-factors of graphs. By our recursive construction, an infinite family of affine-invariant 2-fold quadruple systems is established by using our previous direct construction.
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