The following links are not working and the concepts are also not available. Is it under progress? 4. [Objects and Data Structures](#objects-and-data-structures) 5. [Classes](#classes) 1. [S: Single Responsibility Principle (SRP)](#single-responsibility-principle-srp) 2. [O: Open/Closed Principle (OCP)](#openclosed-principle-ocp) 3. [L: Liskov Substitution Principle (LSP)](#liskov-substitution-principle-lsp) 4. [I: Interface Segregation Principle (ISP)](#interface-segregation-principle-isp) 5. [D: Dependency Inversion Principle (DIP)](#dependency-inversion-principle-dip) 6. [Don’t repeat yourself (DRY)](#dont-repeat-yourself-dry)