What Is Mu?

Fascinating seed questions but first I wonder if Robert really gave away a home? That is a big giveaway. When I see the words "gateless gate" I think of "Gate Gate Para Gate Parasam Gate Bodhi Svaha" - going across a gulf from duality to unity- one form of enlightenment( often fleeting for me) though I see " a living world " constantly and that feels like "awakeness" to me. Every breath I am aware of my connection to the plants who are giving off the oxygen and my contribution to the life and safety and sustainability and joy of my beloved community.