This is a technique sheet rather than a pattern with numbers.
It has a basic crochet instructions as well as the double Filet instructions and although this was written for my workshop at the East London Crochet Group Residential in 2011 experienced crocheters should be able to recreate the double filet version too.
This pattern has only been test crocheted quickly which is why I am offering it for free so any feedback would be welcome.