
theorem Th441:
Sum digits(1120,10) = 4
proof
  thus Sum digits(1120,10) = Sum <%0,2,1%>+Sum <%1%> by Th440,AFINSQ_2:55
  .= Sum <%0,2%> + Sum <%1%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 2) + Sum <%1%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 2 + 1) + Sum <%1%> by AFINSQ_2:53
  .= 3 + 1 by AFINSQ_2:53
  .= 4;
end;
