Volume
218:2 (2005), 379–398
The modular numerical semigroup S(2,6) = 〈3,4,5〉
is pseudo-symmetric. Thus Corollary 60 of the paper is false,
since it asserts that S(a,ab) is not pseudo-symmetric for any
positive integers a,b > 1. The mistake comes from part
(ii) of Proposition 58, which should read
S is pseudo-symmetric if and only if (a−1,b) + (a−1) mod b
= b−1.
(The sign on right-hand side of this equality was
incorrect.)
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