## March 2018 - Solution

Build a graph with 64 vertices (one for every state of the six switches) and edges between any two states that are only one toggle apart. The challenge is to color this graph in five colors (one for each vowel) such that every color appears in each subset of seven vertices, each of which contains a vertex and all its six neighbors. This problem can be solved, for example, using Mixed Integer Programming (MIP) technique, like the CPLEX program written by Alex Fleischer (thanks!).

Andreas Stiller told us that the smallest solution (lexicographically) is AAAAEEEIIIOOUUOUOUIEIAUOEAUAAOIEUOUUOOIIIEEEAAAAEIOAAUAEOUAIEIUO