Juan Pedro Bolívar Puente, Independent Consultant, Sinusoidal Engineering, Germany, gives the first talk in the first panel, Low-level and Systems Programming, on the 2nd day of the ICFP conference. Relaxed Radix Balanced Trees (RRB-Trees) is one of the latest members in a family of persistent tree based data-structures that combine wide branching factors with simple and relatively flat structures. Like the battle-tested immutable sequences of Clojure and Scala, they have ffectively constant lookup and updates, good cache utilization, but also logarithmic concatenation and slicing. Our goal is to bring the benefits of persistent data structures to the discipline of systems programming via generic yet efficient immutable vectors supporting transient batch updates. We describe a C++ implementation that can be integrated in the runtime of higher level languages with a C core (Lisps like Guile or Racket, but also Python or Ruby), thus widening the access to these persistent data structures.