Upgrade lab2 to lab4
Revert "Upgrade lab2 to lab4"

This reverts commit 9a5a3c4197b384d115df76201fef71d2a5628c90.
Revert "Revert "Upgrade lab2 to lab4""

This reverts commit 888961d37dc09c3a1ee79f085cf7933d7d761d7c.
Revert "Revert "Revert "Upgrade lab2 to lab4"""

This reverts commit ea4384cdb3f3b8a38104dba3893556f5289b2365.