This excerpt taken from the MTA 20-F filed May 21, 2009.
(h) (De)/recognized deferred tax on tax losses
Deferred tax asset is recognized on tax losses only to the extent that the realization of the related tax benefit is probable. Deferred tax assets on tax losses that will probably not be recovered are un/de-recognized. On the other hand, when the recoverability of the previously un/derecognized tax losses becomes probable, these deferred tax assets are recognized.