205/264 Notes to the 2017 consolidated financial statements Deferred tax assets are recognized for unused tax losses, unused tax credits, and deductible temporary differences to the extent that it is probable that future taxable profits will be available, against which they can be used. Deferred tax assets are reviewed at each reporting date and are reduced to the extent that it is no longer probable that the related tax benefit will be realized. Deferred tax is measured at the tax rates that are expected to be applied to temporary differences when they reverse, using tax rates enacted or substantively enacted at the reporting date. The measurement of deferred tax reflects the tax consequences that would follow from the manner in which the Group expects, at the reporting date, to recover or settle the carrying amount of its assets and liabilities. Deferred tax assets and liabilities are offset only if certain criteria are met. (iii) Uncertain tax positions In determining the amount of current and deferred income tax, the Group takes into account the impact of uncertain tax positions and whether additional taxes, interest or penalties may be due. This assessment relies on estimates and assumptions and may involve a series of judgments about future events. New information may become available that causes the Group to change its judgment regarding the adequacy of existing tax liabilities. Such changes to tax liabilities will impact tax expense in the period that such a determination is made. (n) Property and equipment Property and equipment are stated at historical cost less accumulated depreciation and any accumulated impairment losses. Historical cost includes any expenditure that is directly attributable to bringing the asset to the location and condition necessary for it to be capable of operating in the manner intended by the Group. The Group adds to the carrying amount of an item of property and equipment the cost of replacing parts of such an item if the replacement part is expected to provide incremental future benefits to the Group. All repairs and maintenance are charged to the consolidated statement of operations during the period in which they are incurred. Depreciation is charged so as to allocate the cost of assets less their residual value over their estimated useful lives, using the straight­line method as follows: • Property and equipment: 3 to 5 years • Leasehold improvements: shorter of the lease term or useful life The assets’ residual values, useful lives, and depreciation methods are reviewed annually and adjusted prospectively if there is an indication of a significant change. An asset’s carrying amount is written down immediately to its recoverable amount if the asset’s carrying amount is greater than its estimated recoverable amount. Gains and losses on disposals are determined by comparing the proceeds with the carrying amount and are recognized in the consolidated statement of operations when the asset is derecognized. (o) Intangible assets Acquired intangible assets other than goodwill comprise acquired developed technology and patents. At initial recognition, intangible assets acquired in a business combination are recognized at their fair value as of the date of acquisition. Following initial recognition, intangible assets are carried at cost less accumulated amortization and impairment losses. F­12