Every mold has its own 300 triplets of numbers, [A,B,C]. A cell with A type is 42 uses a triplet with A number 42.
The first number in this triplet is the type of a new cell that will appear to its left. The second number is the type of new cell that will appear to its front. The third number is the type of new cell that will appear to its right. If any number is -2, then no new cell will appear and the space next to it is empty.