
theorem Th875:
Sum digits(1870,10) = 16
proof
  thus Sum digits(1870,10) = Sum <%0,7,8%>+Sum <%1%> by Th874,AFINSQ_2:55
  .= Sum <%0,7%> + Sum <%8%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 7) + Sum <%8%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 7 + 8) + Sum <%1%> by AFINSQ_2:53
  .= 15 + 1 by AFINSQ_2:53
  .= 16;
end;
