theorem Th88:
  {f,g}**{h,i} = {f*h,f*i,g*h,g*i}
proof
  thus {f,g}**{h,i} = ({f}\/{g})**{h,i} by ENUMSET1:1
    .= ({f}**{h,i}) \/ ({g}**{h,i}) by Th82
    .= {f*h,f*i} \/ ({g}**{h,i}) by Th87
    .= {f*h,f*i} \/ {g*h,g*i} by Th87
    .= {f*h,f*i,g*h,g*i} by ENUMSET1:5;
end;
