array_map_05.sol

pragma solidity ^0.5.3;

contract Mapping {
    
    mapping(address => uint) balances;
    mapping(address => mapping(address => bool)) approved;
    
    function manipulateMapOfMap(spender) external {
        approved[msg.sender][spender] = true                     //assign a value to the approved map
        approved[msg.sender][spender];                           //get the value of the map
        
        delete approved[msg.sender][spender]                     //delete the reference
    }
    
}