reserve FS for non empty doubleLoopStr;
reserve F for Field;
reserve R for Abelian add-associative right_zeroed right_complementable non
  empty addLoopStr,
  x, y, z for Scalar of R;
reserve SF for Skew-Field,
  x, y, z for Scalar of SF;

theorem Th9:
  x<>0.SF implies x * x" = 1.SF & x" * x = 1.SF
proof
  assume x<>0.SF;
  then x"*x = 1_SF by Def2;
  hence thesis by Th7;
end;
