Hey...Explanation 4 to section 43(1) deals with re-acquisition of asset.

It says that if assessee sells some business asset and then re-acquires it, then cost of reacquistion shall be lower of following:

• WDV at time of original transfer, or
• actual price at which such asset is re-acquired

Now lets understand it with help of example...Suppose Reliance buys pollution control equipment for Rs 100,000...Depreciation rate on pollution control equipment is 100%...So, reliance would have claimed 100% depreciation and reduced profit by Rs 100,000...

Now reliance sells this asset to Adani's and then reacquires the same asset again for Rs 100,000...Then as per Explanation 4 to Section 43(1), cost of re-acquired asset in hands of Reliance will be lower of WDV or re-acquired price..In our example, cost of re-acquired asset will be Nil since WDV at the time of orginal transfer was nil..

Hope it suffice your requirement.