sel->tags[arg->i] = !sel->tags[arg->i];
for(i = 0; i < ntags && !sel->tags[i]; i++);
if(i == ntags)
sel->tags[arg->i] = True;
sel->tags[arg->i] = !sel->tags[arg->i];
for(i = 0; i < ntags && !sel->tags[i]; i++);
if(i == ntags)
sel->tags[arg->i] = True;