
theorem Th1328:
Sum digits(4375,10) = 19
proof
  thus Sum digits(4375,10) = Sum <%5,7,3%>+Sum <%4%> by Th1327,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%3%> + Sum <%4%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%3%> + Sum <%4%> by AFINSQ_2:54
  .= (5 + 7 + 3) + Sum <%4%> by AFINSQ_2:53
  .= 15 + 4 by AFINSQ_2:53
  .= 19;
end;
