
theorem Th879:
Sum digits(1914,10) = 15
proof
  thus Sum digits(1914,10) = Sum <%4,1,9%>+Sum <%1%> by Th878,AFINSQ_2:55
  .= Sum <%4,1%> + Sum <%9%> + Sum <%1%> by AFINSQ_2:55
  .= (4 + 1) + Sum <%9%> + Sum <%1%> by AFINSQ_2:54
  .= (4 + 1 + 9) + Sum <%1%> by AFINSQ_2:53
  .= 14 + 1 by AFINSQ_2:53
  .= 15;
end;
