
theorem Th1020:
Sum digits(1334,10) = 11
proof
  thus Sum digits(1334,10) = Sum <%4,3,3%>+Sum <%1%> by Th1019,AFINSQ_2:55
  .= Sum <%4,3%> + Sum <%3%> + Sum <%1%> by AFINSQ_2:55
  .= (4 + 3) + Sum <%3%> + Sum <%1%> by AFINSQ_2:54
  .= (4 + 3 + 3) + Sum <%1%> by AFINSQ_2:53
  .= 10 + 1 by AFINSQ_2:53
  .= 11;
end;
