Revert "Add chapter 4"

This reverts commit 4c538a4e8514f8f70b71e54f5f2a0066db925369.
Revert "Add Responses for chapter 3"

This reverts commit 28ab009ebca3963ddd1fd368ea300b7e865e81b5.
Revert "Revert "Add chapter 4""

This reverts commit 94330dc5114634028abf8eacde837809519e1bac.