theorem Th69:
  for p being FinSequence of 1-tuples_on REAL st len p = 3 holds
  F2M M2F p = p
  proof
    let p be FinSequence of 1-tuples_on REAL;
    assume
A1: len p = 3;
    set q = M2F p;
    q = <* (p.1).1, (p.2).1, (p.3).1 *> by A1,DEF2;
    then len q = 3 & q.1 = (p.1).1 & q.2 = (p.2).1 &
      q.3 = (p.3).1 by FINSEQ_1:45;
    then F2M q = <* <*(p.1).1*>, <*(p.2).1*> , <*(p.3).1*> *> by DEF1;
    hence thesis by A1,Th68;
  end;
