The electronic version of the latest issue of the Girls’ Angle Bulletin is now available on our website.

Through the years, Dr. Kristin Lauter and Microsoft Research have been major financial supporters of Girls’ Angle, especially, our Math Collaboration initiative. Dr. Lauter is a Principal Researcher at Microsoft Research specializing in number theory and cryptography. We are thrilled to embark on a multi-part interview with Dr. Lauter in this issue. The interview was conducted in person by Ke Huang, a graduate student in the department of applied mathematics at the University of Washington. The interview was transcribed by New England Transcription Services with further assistance from Harvard math graduate student Peter Park.

In the previous issue, Prof. Needell showed how unintuitive high-dimensional geometry can be. In this issue’s installment of *Needell in the Haystack*, she exploits this unusual geometry to explain how to solve a problem in compressed sensing. In particular, she uses the fact that a corner of a high-dimensional hyperoctahedron has smaller and smaller high-dimensional solid angle. If you read this article and have trouble seeing this fact about hyperoctahedra, have no fear, Anna investigates the question in Anna’s Math Journal

Next up is a geometric result that Milena Harned, Miriam Rittenberg, and I stumbled upon a little over a year ago. The question is: For a fixed positive integer *n*, what is the locus of points that you can reach in a plane in *n* steps, where a step is one unit long and must have nonnegative vertical displacement. In *Umbrellas, Part 1*, we explain what the locus is for all *n* and prove it for *n* = 1 and 2. In the sequel, we will provide a proof for all *n*.

Harvard undergraduate Michael Kleistra gives us a chance to learn all about cardinality in a step by step installment of *Learn by Doing*.

Emily and Jasmine wrap up their investigation into stacked circles, seeking an elusive container for a stack of circles whose radii form a harmonic progression.

Addie Summer does more math while waiting for a bus.

And we close with a few *Notes from the Club*.

We hope you enjoy it!

Finally, a reminder: when you subscribe to the Girls’ Angle Bulletin, you’re not just getting a subscription to a magazine. You are also gaining access to the Girls’ Angle mentors. We urge all subscribers and members to write us with your math questions or anything else in the Bulletin or having to do with mathematics in general. We will respond. We want you to get active and *do* mathematics. Parts of the Bulletin are written to induce you to wonder and respond with more questions. Don’t let those questions fade away and become forgotten. Send them to us!

We continue to encourage people to subscribe to our print version, so we have removed some content from the electronic version. Subscriptions are a great way to support Girls’ Angle while getting something concrete back in return. We hope you subscribe!