wt_coder * wtc = new wt_coder_binary(bwt,n,am);
alphabetrank = new static_sequence_wvtree(bwt,n,wtc,bmb,am);
delete bmb;
bwt = 0; // already deleted
wt_coder * wtc = new wt_coder_binary(bwt,n,am);
alphabetrank = new static_sequence_wvtree(bwt,n,wtc,bmb,am);
delete bmb;
bwt = 0; // already deleted