and no need to specify them in the contract. It also prevents non-local interactions between the client and the implementation, which makes them easier to understand, maintain, and optimize by the compiler explicitly-marked internal namespace. Aliases in such areas or in .cc files are implementation details (because client code can’t refer to them), and are not restricted by this rule. • Aliases can improve readability in an API, which might make it easier to change the type later. • When placed in a header where client code can refer to them, aliases increase the number of entities in that header’s API, increasing