
theorem Th851:
Sum digits(1584,10) = 18
proof
  thus Sum digits(1584,10) = Sum <%4,8,5%>+Sum <%1%> by Th850,AFINSQ_2:55
  .= Sum <%4,8%> + Sum <%5%> + Sum <%1%> by AFINSQ_2:55
  .= (4 + 8) + Sum <%5%> + Sum <%1%> by AFINSQ_2:54
  .= (4 + 8 + 5) + Sum <%1%> by AFINSQ_2:53
  .= 17 + 1 by AFINSQ_2:53
  .= 18;
end;
