Since the appearance, in 1970, of Vol. I of the present monograph
1370], the theory of bases in Banach spaces has developed
substantially. Therefore, the present volume contains only Ch. III of
the monograph, instead of Ch. Ill, IV and V, as was planned initially
(cp. the table of contents of Vol. I). Since this volume is a
continuation of Vol. I of the same monograph, we shall refer to the
results of Vol. I directly as results of Ch. I or Ch. II (without
specifying Vol. I). On the other hand, sometimes we shall also mention
that certain results will be considered in Vol. III (Ch. IV, V). In
spite of the many new advances made in this field, the statement in the
Preface to Vol. I, that "the existing books on functional analysis
contain only a few results on bases", remains still valid, with the
exception of the recent book [248 a] of J. Lindenstrauss and L.
Tzafriri. Since we have learned about [248 a] only in 1978, in this
volume there are only references to previous works, instead of [248
a]; however, this will cause no inconvenience, since the intersec- tion
of the present volume with [248 a] is very small. Let us also mention
the appearance, since 1970, of some survey papers on bases in Banach
spaces (V. D. Milman [287], [288], C. W. McArthur [275]; M. I.
Kadec [204], § 3 and others).