
theorem Th1148:
Sum digits(1475,10) = 17
proof
  thus Sum digits(1475,10) = Sum <%5,7,4%>+Sum <%1%> by Th1147,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%4%> + Sum <%1%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%4%> + Sum <%1%> by AFINSQ_2:54
  .= (5 + 7 + 4) + Sum <%1%> by AFINSQ_2:53
  .= 16 + 1 by AFINSQ_2:53
  .= 17;
end;
