With this forum, guide http://www.insanelymac.com/forum/topic/285678-lenovo-thinkpad-t420-with-uefi-only/page-25?do=findComment&comment=1952283and my friend Matteo in two days I installed Sierra on lenovo t420, BIOS 1.46, Core i5-3340M 2.7GHz, 4Go DDR3-1600, Intel HD 30000, 1366x768, Sie 10.12.3.