  Let (B_0,B_1) be a Banach pair. Stafney showed that one can replace the space
F(B_0,B_1) with its subspace G(B_0,B_1) in the definition of the norm in the
Calderon complex interpolation method on the strip if the element belongs to
the intersection of the spaces B_i. We shall extend this result to a more
general setting, which contains well-known interpolation methods: the Calderon
complex interpolation method on the annulus, the Lions-Peetre real method (with
several different choices of norms), and the Peetre "plus minus" method.
