message: code review: test if first!=last before dereferencing first
diff: @@ -821,7 +821,7 @@ class Simplex_tree {
  }
  }
  // Next iteration to avoid consecutive equal values
  - while ((vertex_one == *first) && (first < last)) {
  + while ((first < last) && (vertex_one == *first)) {
  ++first;
  }
  // End of insertion
  