aave-protocol-v2/contracts/tokenization/interfaces/IScaledBalanceToken.sol

// SPDX-License-Identifier: agpl-3.0
pragma solidity ^0.6.8;

interface IScaledBalanceToken {
  /**
   * @dev returns the principal balance of the user. The principal balance is the last
   * updated stored balance, which does not consider the perpetually accruing interest.
   * @param user the address of the user
   * @return the principal balance of the user
   **/
  function scaledBalanceOf(address user) external view returns (uint256);

  /**
   * @dev returns the principal balance of the user and principal total supply.
   * @param user the address of the user
   * @return the principal balance of the user
   * @return the principal total supply
   **/
  function getScaledUserBalanceAndSupply(address user) external view returns (uint256, uint256);

  /**
   * @dev Returns the scaled total supply of the variable debt token. Represents sum(borrows/index)
   * @return the scaled total supply
   **/
  function scaledTotalSupply() external view returns (uint256);
}