6 B. JAWERTH AND M. MILMAN
and B are two Banach spaces, then we write A = B if they are the same, A « B
means that they are the same as vector spaces with comparable norms. A denotes
the Gagliardo completion of A in E(A), and A° is the closure of A(A) in A. As
usual, C and c denote constants that might be different on each appearance.