Form.html

<html>
    <head>
        <title>Form</title>
        <script>
        </script>
    </head>
    <body>


        <form action="switch2.php" method="POST" name="dati" id="form1">
            <p>Lettera </p><input type="text" id="Lettera" name="Lettera" required pattern="[a-zA-Z]*" maxlength="1" placeholder="Lettera">
            <br>
            <input type="submit" value="Lettera">
        </form>
    </body>
</html>