reserve X for set;
reserve k,m,n for Nat;
reserve i for Integer;
reserve a,b,c,d,e,g,p,r,x,y for Real;
reserve z for Complex;

theorem Lm15:
  for f being real-valued FinSequence holds len cosec f = len f
  proof
    let f be real-valued FinSequence;
    dom cosec f = dom f by Def4;
    hence thesis by FINSEQ_3:29;
  end;
