theorem Th87:
  {f}**{h,i} = {f*h,f*i}
proof
  thus {f}**{h,i} = {f}**({h}\/{i}) by ENUMSET1:1
    .= ({f}**{h}) \/ ({f}**{i}) by Th82
    .= {f*h} \/ ({f}**{i}) by Th86
    .= {f*h} \/ {f*i} by Th86
    .= {f*h,f*i} by ENUMSET1:1;
end;
