Bipartite Networks $-$ General Considerations

Consider a bipartite network with N$1$ and N$2$ nodes in the two sets.

What is the maximum number of links Lmax the network can have?

How many links cannot occur compared to a non$-$bipartite network of size N $=$ N$1+$ N$2?$

If N$1$N$2,$ what can you say about the network density, that is the total number of links over the maximum number of links, Lmax?

Find an expression connecting N$1,$ N$2$ and the average degree for the two sets in the bipartite network, k$1$ and k$2.$