The article explores how competition between companies affects the variety of products available to consumers. It first looks at how single-product companies compete with each other, then extends this to companies that offer multiple products. The researchers found that when products are very different from each other or when it's not very efficient to produce multiple products, competition between single-product companies can be similar to competition between companies with multiple products. This means that the variety of products available to consumers can be influenced by how companies compete with each other.