Any experts on the "Heise Method" around ?
I need some help on the "down under" strategy for "inserting 3 edges" in the "two pairs" approach.
I can see what the algorithm does, but I do not understand it to the same depth as the other strategies used by the method, and I can't really apply it.

In addition I send some configurations I ran into where I can't see an efficient way out using the Heise method, maybe someone can advise:

1) U2 B F2 D' F D' F' D' F D2 B' F U2
2) B2 L F' L F L2 B R' U2 R U2 B U2
3) B2 D B' U' B D' B2 U R' B' R B R
4) L F' L D2 R' B R' U2 B' R2 D2

My goal is to be able to do a linear solve on every cube (ok 90% would be enough) with less then 50 moves (HTM) and only with algorithms I fully understand.