
theorem Th1356:
Sum digits(4725,10) = 18
proof
  thus Sum digits(4725,10) = Sum <%5,2,7%>+Sum <%4%> by Th1355,AFINSQ_2:55
  .= Sum <%5,2%> + Sum <%7%> + Sum <%4%> by AFINSQ_2:55
  .= (5 + 2) + Sum <%7%> + Sum <%4%> by AFINSQ_2:54
  .= (5 + 2 + 7) + Sum <%4%> by AFINSQ_2:53
  .= 14 + 4 by AFINSQ_2:53
  .= 18;
end;
