This paper is mainly
concerned with generalisations of Hörmander’s results on multipliers from Lp(Rn)
to Lq(Rn) (see Hörmander [6]). Our principal results are that Hörmander’s
Theorem 1.12 and Corollary 1.5 continue to hold for any LCA group with an infinite
discrete subgroup. In order to establish and formulate our results, we define the
Fourier transform of functions in Lp(G) where 1 ≦ p ≦∞ and G is any LCA group.
Here we use the author’s work on quasimeasures in “Quasimeasures and operators
commuting with convolution” [4].