But it is claimed that the order is unreasonable in that it not only requires the building to be vacated, but also prohibits its use as a human habitation at any future time without written permission of the board; so that even if the plaintiff should remedy the' evils which the board has found to exist, and should restore the premises to a sanitary condition, she would still be prevented from enjoying her property.. The answer to this seems to be that the . order is to be construed' as applying to then existing conditions. It will be time enough to consider what the rights of the plaintiff may be when she has removed all present grounds for complaint. She would then be in a position to apply for the permission which the order contemplates, and, if the nuisance has been abated, it must be assumed that the board would grant it. Indeed, it could not legally withhold it. The statute (section 659 of the Consolidation Act) under which the order in question was made provides that the board may revoke the order whenever it “ shall become satisfied that the danger from said building or part thereof has ceased to exist, or that said building has been repaired so as to be habitable.” It could not capriciously or unreasonably refuse to be satisfied where the facts plainly demand such a conclusion. Although the words which confer the power to revoke are permissive in form, they import, under well-settled rules, an .obligation to exercise such power when the justice of the case demands it. In other words, the deprivation of which the plaintiff complains continues only so long as the conditions exist which justified the order in the first instance, and the plaintiff, therefore, is not aggrieved, on constitutional or other grounds, by the operation of repressive measures essential to