# Yulia Khalniyazova - Taiga Book - Validity Predicates (Highlights) ![rw-book-cover|256](https://readwise-assets.s3.amazonaws.com/media/uploaded_book_covers/profile_155788/taiga) ## Highlights - A **validity predicate** is a piece of code defined by an application that authorizes transactions the application is involved in. ([View Highlight](https://read.readwise.io/read/01hcv2qczyvq3wjdy7gfy8g3nr)) ^611213926 similar: CKB types cript - Validity predicates in Taiga have a hierarchical structure. For all applications involved in a transaction, their `ApplicationVP` must be checked. These VPs might require validity of some other VPs in order for a transaction to be considered valid. In that case, those other VPs must be checked too. ([View Highlight](https://read.readwise.io/read/01hcv2sdq5pzj2ccwx8rwjvven)) ^611214126 CKB lacks of a type script hierarchical structure.