function eraseconc(M,N)
curd = pwd;
cd ../string_proc/combinatorics/
addpcurdir
cd(curd)

T = 1e8;
% indep
%M = 10;
%N = 6;
alf = 'ab';
p = (M-N)/M;

DEV = [];

E = round(indepExp(M,N));

for t=1:T
  x = get_datum(alf,M);
  y = get_datum(alf,N);
  
  X = count_subseq(x,y);
  
  if X>2*E
    DEV(end+1) = (X-E);

  hist(DEV,sqrt(length(DEV)));
 
  drawnow
end
end

return

function y = rand_erase(x,N)
ii = randperm(length(x));
ii = ii(1:N);
ii = sort(ii);
y = x(ii);
return
y = [];
for i=1:length(x)
  if rand > p
    y(end+1) = x(i);
  end
end
return

function x = get_datum(alf,n)
na = length(alf);
x = alf(ceil(rand(1,n)*na));
return

function E = indepExp(M,N)
E = exp(logchoose(M,N) + N*log(1/2));
return