Morpion Solitaire 5D: a new upper bound of 121 on the maximum score

Understand

Morpion Solitaire is a pencil-and-paper game for a single player.

• A move in this game consists of putting a cross at a lattice point and then drawing a line segment that passes through exactly five consecutive crosses.
• The objective is to make as many moves as possible, starting from a standard initial configuration of crosses.
• For one of the variants of this game, called 5D, we prove an upper bound of 121 on the number of moves.