
theorem Th537:
Sum digits(2080,10) = 10
proof
  thus Sum digits(2080,10) = Sum <%0,8,0%>+Sum <%2%> by Th536,AFINSQ_2:55
  .= Sum <%0,8%> + Sum <%0%> + Sum <%2%> by AFINSQ_2:55
  .= (0 + 8) + Sum <%0%> + Sum <%2%> by AFINSQ_2:54
  .= (0 + 8 + 0) + Sum <%2%> by AFINSQ_2:53
  .= 8 + 2 by AFINSQ_2:53
  .= 10;
end;
