
theorem Th1022:
Sum digits(1357,10) = 16
proof
  thus Sum digits(1357,10) = Sum <%7,5,3%>+Sum <%1%> by Th1021,AFINSQ_2:55
  .= Sum <%7,5%> + Sum <%3%> + Sum <%1%> by AFINSQ_2:55
  .= (7 + 5) + Sum <%3%> + Sum <%1%> by AFINSQ_2:54
  .= (7 + 5 + 3) + Sum <%1%> by AFINSQ_2:53
  .= 15 + 1 by AFINSQ_2:53
  .= 16;
end;
