6 B. JAWERTH AND M. MILMAN

and B are two Banach spaces, then we write A = B if they are the same, A « B

v

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.