Let m be a tempered
distribution on Rn. We say m is an Lp, Lq multiplier (more briefly: m ∈ Mpq) if, for
each ϕ ∈𝒮, the inverse Fourier transform of mϕ is in Lq, and there is a constant C
such that ∥ℱ−1(mϕ)∥q≦ C∥ϕ∥p for all such ϕ. The basic problem we shall consider
is that of establishing sufficient conditions that a locally integrable function m ∈ Mpq
in the case 1 < p < q < ∞.