
theorem Th859:
Sum digits(1672,10) = 16
proof
  thus Sum digits(1672,10) = Sum <%2,7,6%>+Sum <%1%> by Th858,AFINSQ_2:55
  .= Sum <%2,7%> + Sum <%6%> + Sum <%1%> by AFINSQ_2:55
  .= (2 + 7) + Sum <%6%> + Sum <%1%> by AFINSQ_2:54
  .= (2 + 7 + 6) + Sum <%1%> by AFINSQ_2:53
  .= 15 + 1 by AFINSQ_2:53
  .= 16;
end;
