theorem Th100:
  {a,b}**{s,t} = {a*s,a*t,b*s,b*t}
proof
  thus {a,b}**{s,t} = ({a}\/{b})**{s,t} by ENUMSET1:1
    .= ({a}**{s,t}) \/ ({b}**{s,t}) by Th92
    .= {a*s,a*t} \/ ({b}**{s,t}) by Th99
    .= {a*s,a*t} \/ {b*s,b*t} by Th99
    .= {a*s,a*t,b*s,b*t} by ENUMSET1:5;
end;
