theorem Th99:
  {a}**{s,t} = {a*s,a*t}
proof
  thus {a}**{s,t} = {a}**({s}\/{t}) by ENUMSET1:1
    .= ({a}**{s}) \/ ({a}**{t}) by Th92
    .= {a*s} \/ ({a}**{t}) by Th98
    .= {a*s} \/ {a*t} by Th98
    .= {a*s,a*t} by ENUMSET1:1;
end;
