reserve a,b,c,d,e,f for Real,
        k,m for Nat,
        D for non empty set,
        V for non trivial RealLinearSpace,
        u,v,w for Element of V,
        p,q,r for Element of ProjectiveSpace(V);
reserve o,p,q,r,s,t for Point of TOP-REAL 3,
        M for Matrix of 3,F_Real;
reserve pf for FinSequence of D;
reserve PQR for Matrix of 3,F_Real;

theorem Th61:
  width <*pf*> = len pf
  proof
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 thesis by A1,MATRIX_0:def 3;
end;
