
theorem Th841:
Sum digits(1452,10) = 12
proof
  thus Sum digits(1452,10) = Sum <%2,5,4%>+Sum <%1%> by Th840,AFINSQ_2:55
  .= Sum <%2,5%> + Sum <%4%> + Sum <%1%> by AFINSQ_2:55
  .= (2 + 5) + Sum <%4%> + Sum <%1%> by AFINSQ_2:54
  .= (2 + 5 + 4) + Sum <%1%> by AFINSQ_2:53
  .= 11 + 1 by AFINSQ_2:53
  .= 12;
end;
