various methods of joining hairpin lace crochet - some a sort of cable using no extra yarn, others basic crochet stitches; just had another look - this is hairpin heaven! scores of detailed charts, pics on hairpin techniques & ideas.
Hairpin lace variations. In Russian but with clear crochet schemes and pictures.
Kum Boncukla Firkete Oyası Yazma Nasıl Yapılır? - YouTube