
theorem Th1038:
Sum digits(1587,10) = 21
proof
  thus Sum digits(1587,10) = Sum <%7,8,5%>+Sum <%1%> by Th1037,AFINSQ_2:55
  .= Sum <%7,8%> + Sum <%5%> + Sum <%1%> by AFINSQ_2:55
  .= (7 + 8) + Sum <%5%> + Sum <%1%> by AFINSQ_2:54
  .= (7 + 8 + 5) + Sum <%1%> by AFINSQ_2:53
  .= 20 + 1 by AFINSQ_2:53
  .= 21;
end;
