The market's buy command is used to set prices for FRPs of a
particular kind. In particular, it can be used to estimate the
risk-neutral prices of FRPs and kinds.

The syntax of the command is

  buy _count_ @ _prices_ with kind (___).

Here, _count_ is a positive integer (like 1000); you can use _ as a
separator between blocks of three digits. Also, _prices_ is a
comma-separated list of numbers, with an optional sign and an
optional leading $. And ___ should be filled with the specification
of a kind (see `help kinds`).

The output includes a display of the specified kind
and a table summarizing the purchases. The table has one
row per specified price, in order, and shows the price per unit,
the total net payoff from the purchase of all the FRPs,
and the net payoff per unit.
