Among other things, someone was bound to notice that the interaction between increasing returns and product differentiation could help explain some puzzles about international trade--like why most trade is between seemingly similar countries.
There are puzzles about international trade.
Everyone understands everything about international trade.
A person plays the guitar.
The woman is reading a newspaper.
The man is outdoors.
Two boys are running.
Someone is playing a game outdoors.
There was a powerful earthquake in 1995.