g = Associative Array();
g[1] = Associative Array({1, 2, 4});
g[2] = Associative Array({1, 3});
g[3] = Associative Array({4, 5});
g[4] = Associative Array({4, 5});
g[5] = Associative Array({1, 2});
This is a two-level associative array. The associative array g contains five associative arrays (1, 2, 3, 4, and 5). In the containing array g, both the keys (1-5) and the values (the arrays that define the map) are important. In the inner associative arrays, the values do not matter. Only the keys are important.
Figure 6.2 Example of a Directed Graph
dfs = Function( {ref, node, visited},
    {chnode, tmp},
    Write( "\!NNode: ", node, ", ", ref[node] << Get Keys );
    visited[node] = 1;
    tmp = ref[node];
    chnode = tmp << first;
    While( !Is Missing( chnode ),
        If( !visited[chnode],
            visited = Recurse( ref, chnode, visited )
        );
        chnode = tmp << Next( chnode );
    );
    visited;
);
Notes: 
dfs( g, 2, J( N Items( g << Get Keys ), 1, 0 ) );
Node 2: {1, 3}
Node 1: {1, 2, 4}
Node 4: {4, 5}
Node 5: {1, 2}
Node 3: {4, 5}
[1, 1, 1, 1, 1]
New Window( "Directed Graph",
	Graph Box(
		Frame Size( 300, 300 ),
		X Scale( -1.5, 1.5 ),
		Y Scale( -1.5, 1.5 ),
		Local( {n = N Items( g ), k = 2 * Pi() / n, r, i, pt, from, to,
			edge, v, d},
			Fill Color( "green" );
			Pen Size( 3 );
			r = 1 / (n + 2);
			For( i = 1, i <= n, i++,
				pt = Eval List( {Cos( k * i ), Sin( k * i )} );
				edges = g[i];
				For( edge = edges << First, !Is Empty( edge ),
					edge = edges << Next( edge ),
					to = Eval List( {Cos( k * edge ), Sin( k * edge )} );
					If( i == edge,
						Circle( Eval List( 1.2 * pt ), 0.9 * r ), 	// else
						v = pt - to;
						d = Sqrt( Sum( v * v ) );
						{from, to} = Eval List(
							{pt * (d - r) / d + to * r / d, pt * r / d + to *
								(d - r) / d}
						);
						Arrow( from, to );
					);
				);
				Circle( pt, r, "fill" );
				Text( Center Justified, pt - {0, 0.05}, Char( i ) );
			);
		)
	)
);

Help created on 10/11/2018