# Composite Operations

In order to perform arbitrary actions with borrowed funds, Concordia allows for composite operations.  A user may perform any sequence of operations in a single **atomic transaction** so long as the user’s portfolio is healthy at the conclusion of the transaction.  This loose constraint – that the portfolio is healthy at the conclusion of the transaction – allows for the portfolio to become unhealthy at any point during the transaction.

#### An example of composite actions is performing a “margin trade.”   In this situation, the user is able to perform a composite operation where they:

1. Withdraw the entirety of their portfolio
2. Trade the withdrawn capital for another asset
3. Deposit that different asset into their portfolio

For example: suppose a user has $4 of ETH in their account, with $2 of equity.  In this situation, the portfolio is 2x leveraged.  They have access to twice as much value as their equity.  In other words, half of their portfolio's value is a liability.  The user wants to trade the ETH for USDT at 2x leverage (essentially shorting ETH).  

In one transaction: they **withdraw** all $4 of ETH, swap it for \~$4 of USDC, and **deposit** the \~$4 USDC into their portfolio.  At the conclusion of this transaction, this portfolio has $2 of ETH liability and $4 of USDC deposited.  

This kind of leveraged trade would not be possible without the ability to compose operations in a single transaction, since the withdrawal of all $4 ETH makes the portfolio unhealthy – though only “temporarily” when immediately followed by a deposit of $4.

#### The most common pattern for composite operations is to perform an action with borrowed funds.  They generally will take the shape of:

1. Borrow an asset in order to lever up one’s holdings
2. Withdraw assets from a portfolio (making it “temporarily” under-collateralized)
3. Perform an operation – or several – on a 3rd-party protocol with these withdrawn assets
4. Deposit a new sum of assets into the portfolio, restoring its health from the withdrawal at Step 2.

But any operation on Concordia can be composed with others in a single transaction.  Application developers are free to create useful compositions to create convenient financial products for users.  Programming a composite instruction has blockchain specific requirements.  Please see the developer documentation for instructions on how to create multi-operation transactions.