Gregory has this to say about Tronc Commun: Tronc commun is based on the following idea: the two main pieces are common to the three puzzles: TC1, TC2 and TC3. I named those 2 main pieces tronc commun (common core in English) The common core is surrunded by 3 different sets of pieces forming TC1, TC2 and TC3. The level of difficulty increases with the number. One is easier, and Three is very very difficult. Finding the exact move to assemble the first three pieces of TC3 pieces is more than complex and the puzzler must be exactly precise.
Construction of this puzzle is excellent with very close tolerances. Fit is excellent at moderate humidity.
42 copies made for sale, each signed and dated. This puzzle is shipped disassembled.
This puzzle has three levels of difficulty. Level 1 is not so easy. This version has the most pieces (8) and eventually I resorted to BurrTools (no rotations). Level 2 goes down to 6 pieces but thankfully involves only one rotation. I attempted level 3 (6 pieces) but was never able to get anywhere on it. One of the pieces forms a loop, which draws fear in the eyes of any solver when you see where it has to go.
Fast forward two years. Stuck at home in the pandemic I gave this another whirl. Solved 1 again, but on 2 I broke a piece. After gluing it I decided to give 3 a whirl. Fearing another breakage, I looked online and found a beautiful solution video by "eriban". Using the video, I solved the puzzle, but I doubt I could have done it without help.