Compulsory 1 (beginning of Grade One) → Compulsory 4 (end of Grade One) → Compulsory 5 (beginning of Grade One) → Compulsory 2 (end of Grade One) → Compulsory 3.

Some things in compulsory 5 can't be used until compulsory 2 is completed.

As for why it is so complicated, the researchers say it is in the order of the old textbooks.