//! Module graph contains graph structures.
//!
//! # Basic usage:
//!
//! ```
//! use snark_tool::graph::graph::{Graph, GraphConstructor};
//! use snark_tool::graph::undirected::simple_graph::graph::SimpleGraph;
//!
//! fn main() {
//! let mut graph = SimpleGraph::new();
//! graph.add_edge(0, 5);
//! graph.add_edge(2, 4);
//!
//! for edge in graph.edges() {
//! println!("{:?}", edge);
//! }
//! }
//! ```