let D be non empty set ; :: thesis: for pf being FinSequence of D holds width <*pf*> = len pf
let pf be FinSequence of D; :: thesis: width <*pf*> = len pf
A1: len <*pf*> = 1 by FINSEQ_1:39;
rng <*pf*> = {pf} by FINSEQ_1:39;
then pf in rng <*pf*> by TARSKI:def 1;
hence width <*pf*> = len pf by A1, MATRIX_0:def 3; :: thesis: verum