I was intrigued by this comment and went searching for this. From this FastCompany article it's inspired by Futura and Univers though sounds like it's more or less a custom job:
> At the time, Lindon was "in love with two bold fonts" known as Univers 67, which is a condensed bold type, and Futura Bold. He takes me through how he started playing with the two typefaces and the letter spacing, from extremely wide to locked together, uppercase and lowercase, mixing and tinkering. One iteration had a capital E and a lowercase x: "I started squeezing the letter spacing, I saw a white arrow start to appear between the E and the x. I thought, ‘There’s something there.’ I tried both fonts, but I didn’t like how much I had to distort either typeface to make the arrow look good. I thought, ‘Would it be possible to blend the best features of both?’ I took the high x of Univers and mixed it with the stroke of Futura Bold. The x rose to the crossbar of a lowered E. I kept tweaking, and eventually not only did the arrow look natural and unforced, but I ended up with a whole new letterform."
