Is mapping from simplified to traditional characters injective (one-to-one function)?
One simplified character may mapping to multiple traditional ones:


皇后 -> 皇后，後天 -> 后天
頭髮 -> 头发，發財 -> 发财


As reversed, one traditional character may mapping to multiple simplified ones too:


乾燥 -> 干燥，乾隆 -> 乾隆
瞭望 -> 瞭望，瞭解 -> 了解


This wikipedia article had discussed such thing for further reading: https://en.wikipedia.org/wiki/Ambiguities_in_Chinese_character_simplification