
theorem Th1360:
Sum digits(4775,10) = 23
proof
  thus Sum digits(4775,10) = Sum <%5,7,7%>+Sum <%4%> by Th1359,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%7%> + Sum <%4%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%7%> + Sum <%4%> by AFINSQ_2:54
  .= (5 + 7 + 7) + Sum <%4%> by AFINSQ_2:53
  .= 19 + 4 by AFINSQ_2:53
  .= 23;
end;
