a−[a−b+a−{a−(a−b−a)}]
= a−[a−b+a−{a−(a−b+a)}]
= a−[a−b+a−{a−(a+a−b)}]
= a−[a−b+a−{a−(2a−b)}]
= a−[a−b+a−{a−2a+b}]
= a−[a−b+a−{−a+b}]
= a−[a−b+a+a−b]
= a−[a−b−a+a−b]
= a−[(a−a+a)+(−b−b)]
= a−[a+(−2b)]
= a−[a−2b]
= a−a+2b
= 2b
Hence, a−[a−b+a−{a−(a−b−a)}]=2b
