How to call a class in your Slim Framework?

$app->get('/', function (Request $request, Response $response, array $args) {
 $response->getBody()->write("Main"); // works

 $mod = \Model\MyModel();
$mod->go();

 return $response;
});

The startup class via Composer connected:

"autoload": {
 "psr-4": {
 "Model\\": "model/"
}
 }

On the screen error, the error and the namespace and class name written in lowercase letters, and my name was the title:

Fatal error: Call to undefined function model\mymodel() in

Tried the class and namespace name to lowercase did not help. But still I wonder why, he had them somewhere inside converts?