<?php

$autors = [
'Толстой Л.Н.' => [
	'info' => [
		'birthday' => 1828,
		'mail' => 'tolstoy@pochta.net'
	],
	'books' => [
		'name' => 'Семейное счастье', 'date' => 1859,
		'name' => 'Война и мир', 'date' => 1869,
		'name' => 'Анна Каренина', 'date' => 1877
	]
]];

$key = array_keys($autors)[0];
echo $key . ' ' . $autors[$key]['info']['mail'] . ' ' . $autors[$key]['info']['birthday'];