
theorem Th893:
Sum digits(2090,10) = 11
proof
  thus Sum digits(2090,10) = Sum <%0,9,0%>+Sum <%2%> by Th892,AFINSQ_2:55
  .= Sum <%0,9%> + Sum <%0%> + Sum <%2%> by AFINSQ_2:55
  .= (0 + 9) + Sum <%0%> + Sum <%2%> by AFINSQ_2:54
  .= (0 + 9 + 0) + Sum <%2%> by AFINSQ_2:53
  .= 9 + 2 by AFINSQ_2:53
  .= 11;
end;
