EXAMPLE
.......\LESSON1
.......\LESSON10
.......\........\L10_1.C
.......\........\L10_10.C
.......\........\L10_11.C
.......\........\L10_12.C
.......\........\L10_2.C
.......\........\L10_3.C
.......\........\L10_4.C
.......\........\L10_5.C
.......\........\L10_6.C
.......\........\L10_7.C
.......\........\L10_8.C
.......\........\L10_9.C
.......\LESSON11
.......\........\L11_1.C
.......\........\L11_10.C
.......\........\L11_2.C
.......\........\L11_3.C
.......\........\L11_4.C
.......\........\L11_5.C
.......\........\L11_6.C
.......\........\L11_7.C
.......\........\L11_8.C
.......\........\L11_9.C
.......\LESSON12
.......\........\L12_1.C
.......\........\L12_2.C
.......\........\L12_3.C
.......\........\L12_4.C
.......\........\L12_5.C
.......\........\L12_6.C
.......\........\L12_7.C
.......\........\L12_8.C
.......\........\L12_9.C
.......\LESSON13
.......\........\L13_1.C
.......\........\L13_2.C
.......\........\L13_3.C
.......\........\L13_4.C
.......\........\L13_5.C
.......\........\L13_6.C
.......\........\L13_7.C
.......\........\L13_8.C
.......\........\L13_9.C
.......\LESSON14
.......\........\L14_1.C
.......\........\L14_10.C
.......\........\L14_2.C
.......\........\L14_3.C
.......\........\L14_4.C
.......\........\L14_5.C
.......\........\L14_6.C
.......\........\L14_7.C
.......\........\L14_8.C
.......\........\L14_9.C
.......\.......\L1_1.C
.......\.......\L1_2.C
.......\.......\L1_3.C
.......\.......\L1_4.C
.......\.......\L1_5.C
.......\.......\L1_6.C
.......\.......\L1_7.C
.......\.......\L1_8.C
.......\.......\L1_9.C
.......\LESSON2
.......\.......\L2_1.C
.......\.......\L2_2.C
.......\.......\L2_3.C
.......\.......\L2_4.C
.......\.......\L2_5.C
.......\.......\L2_6.C
.......\.......\L2_7.C
.......\.......\L2_8.C
.......\LESSON3
.......\.......\L3_1.C
.......\.......\L3_2.C
.......\.......\L3_3.C
.......\.......\L3_4.C
.......\.......\L3_5.C
.......\.......\L3_6.C
.......\.......\L3_7.C
.......\.......\L3_8.C
.......\LESSON4
.......\.......\L4_1.C
.......\.......\L4_10.C
.......\.......\L4_11.C
.......\.......\L4_12.C
.......\.......\L4_13.C
.......\.......\L4_2.C
.......\.......\L4_3.C
.......\.......\L4_4.C
.......\.......\L4_5.C
.......\.......\L4_6.C
.......\.......\L4_7.C
.......\.......\L4_8.C
.......\.......\L4_9.C
.......\LESSON5
.......\.......\L5_1.C