theorem
  len F = 2 implies g "**" F = g.(F.1,F.2)
proof
  assume
A1: len F = 2;
  then F = <* F.1,F.2 *> by FINSEQ_1:44
    .= <* F/.1,F.2 *> by A1,FINSEQ_4:15
    .= <* F/.1,F/.2 *> by A1,FINSEQ_4:15;
  hence g "**" F = g.(F/.1,F/.2) by Th12
    .= g.(F.1,F/.2) by A1,FINSEQ_4:15
    .= g.(F.1,F.2) by A1,FINSEQ_4:15;
end;
