
theorem Th1180:
Sum digits(2050,10) = 7
proof
  thus Sum digits(2050,10) = Sum <%0,5,0%>+Sum <%2%> by Th1179,AFINSQ_2:55
  .= Sum <%0,5%> + Sum <%0%> + Sum <%2%> by AFINSQ_2:55
  .= (0 + 5) + Sum <%0%> + Sum <%2%> by AFINSQ_2:54
  .= (0 + 5 + 0) + Sum <%2%> by AFINSQ_2:53
  .= 5 + 2 by AFINSQ_2:53
  .= 7;
end;
