:: deftheorem Def1 defines the_set_of_l1ComplexSequences CSSPACE3:def 1 :
for b₁ being Subset of Linear_Space_of_ComplexSequences holds
( b₁ = the_set_of_l1ComplexSequences iff for x being object holds
( x in b₁ iff ( x in the_set_of_ComplexSequences & seq_id x is absolutely_summable ) ) );