1.- Many thanks to the Two Moon Tango website ( http://www.twomoontango.com/ ) for this comprehensive description on its "Codes of the Dance" page

2.- Terpsichoral Tangoaddict | Facebook website -The Art of Long-Range Mirada/Cabeceo https://www.facebook.com/terpsichoral.tangoaddict/posts/762887170471352?fref=nf