Autumn 2021 Sesshin Day 5: Ummon's "One Treasure"

In Autumn Sesshin's Day Five Teisho, given on Oct. 6th, 2021, Rinzan Osho examines The Hekiganroku, Ummon's "One Treasure." Hidden in the mountain of form is one treasure. How do we know it? How do we testify to it?