They are not going to "Buy Back" shares. The reduction in AS is made available as a result of the reverse split. Once a reverse split is done you can reduce the AS in some multiple up to the amount of the reverse split. If they do a 1:10 reverse split then they can also do a 1:10 reduction of the AS. They don't have to, but they can. They will probably do a reverse split and then reduce the AS by about half of that multiple. In that scenario the AS would be reduced by 1:5.