
theorem Th869:
Sum digits(1804,10) = 13
proof
  thus Sum digits(1804,10) = Sum <%4,0,8%>+Sum <%1%> by Th868,AFINSQ_2:55
  .= Sum <%4,0%> + Sum <%8%> + Sum <%1%> by AFINSQ_2:55
  .= (4 + 0) + Sum <%8%> + Sum <%1%> by AFINSQ_2:54
  .= (4 + 0 + 8) + Sum <%1%> by AFINSQ_2:53
  .= 12 + 1 by AFINSQ_2:53
  .= 13;
end;
