There are a number of compression locks in grappling, which function with tori placing a limb (acting as a fulcrum) in the crook of one of uke's joints, and applying pressure to flex the joint over the limb, simultaneously crushing the muscles/ligaments either side of it and hyper-flexing the joint around it.
While Achilles Locks (ashi-hishigi, targetting the ankle joint), Calf/Thigh Slicers (hiza-hishigi etc, targeting the knee joint), and even neck locks (kubi-hishigi etc) are formal judo techniques (if banned in randori/competition for over a century), I have never seen the Biceps Slicer described as an explicit technique in any Kodokan judo material.1
Is a biceps slicer a legal technique (since it is a joint lock targeting the elbow), and if not, was it ever taught in judo?
1. Here it is being demonstrated in a Kosen Judo club however, using pressure from a leg triangle to apply the lock. And here being demonstrated by John Anderson (Kodokan 8th Dan), using pressure from the other arm.