Let K be a Calderon-Zygmund
singular integral operator with smooth kernel. That is, there is an Ω(x) defined on
Rn∖{0} which satisfies
∫|x|=1Ω = 0,Ω≢0,
Ω(rx) = Ω(x)when r > 0and x ∈ Rn∖{0},
|Ω(x) − Ω(y)|≤|x − y|when|x| = |y| = 1,
(*)
and that
Let
R. Coifman, R. Rochberg and G. Weiss showed the weak version of the factorization
theorem of H1(Rn) and that was refined by Uchiyama in the following
form.