
theorem Th451:
Sum digits(1220,10) = 5
proof
  thus Sum digits(1220,10) = Sum <%0,2,2%>+Sum <%1%> by Th450,AFINSQ_2:55
  .= Sum <%0,2%> + Sum <%2%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 2) + Sum <%2%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 2 + 2) + Sum <%1%> by AFINSQ_2:53
  .= 4 + 1 by AFINSQ_2:53
  .= 5;
end;
