We give a self-contained presentation of Hard Interaction, a rewriting system on fixed graphs. We discuss the universality of natural subclasses of hard systems and highlight the main ideas that lead to a universal system with 7 rules called Hard Combinators.

This paper presents a simple implementation of the λ-calculus in the interaction net paradigm. It is based on a two-fold translation. λ-terms are coded (for duplication) or decoded (for execution), and reduction is achieved by switching between these two states: decoding corresponds to head reduction and encoding to left reduction.

We present a graphical environment for parallel object-oriented programming. It provides visual tools to develop and debug object-oriented programs as well as parallel or concurrent systems. This environment was derived from a structural operational semantics of an extension of the Eiffel language, Eiffel//. Object-related features of the language (inheritance, polymorphism) are formalized using a big-step semantics, while the interleaving model of concurrency is expressed with small-step semantics.Without user instrumentation, the interactive environment proposes features such as step-by-step animated executions, graphical visualization of object and process topology, futures and pending requests, control of interleaving, deadlock detection.