“[T]he Agency will begin with each product (narrowly defined) produced or sold by each merging firm and ask what would happen if a hypothetical monopolist of that product imposed at least a "small but significant
and nontransitory" increase in
price, but the terms of sale of all other
products remained constant. If, in response to the price increase, the reduction in sales of the product
would be large enough that a hypothetical
monopolist would not find it profitable to impose
such an increase in price, then the Agency will
add to the product group the product that is the next-best substitute for the merging firm's
product.”
