5    11    7     3    5    4    7     11    4    9

            5 11 7 3 5 4 7 11 4 9 
            merge_sort(a,0,4)
            merge_sort(a,0,2)
            merge_sort(a,0,1)
            merge_sort(a,0,0)
            merge_sort(a,1,1)
            merge(a,0,0,1)         a = 5 11 7 3 5 4 7 11 4 9 
            merge_sort(a,2,2)
            merge(a,0,1,2)         a = 5 7 11 3 5 4 7 11 4 9 
            merge_sort(a,3,4)
            merge_sort(a,3,3)
            merge_sort(a,4,4)
            merge(a,3,3,4)         a = 5 7 11 3 5 4 7 11 4 9 
            merge(a,0,2,4)         a = 3 5 5 7 11 4 7 11 4 9 
            merge_sort(a,5,9)
            merge_sort(a,5,7)
            merge_sort(a,5,6)
            merge_sort(a,5,5)
            merge_sort(a,6,6)
            merge(a,5,5,6)         a = 3 5 5 7 11 4 7 11 4 9 
            merge_sort(a,7,7)
            merge(a,5,6,7)         a = 3 5 5 7 11 4 7 11 4 9 
            merge_sort(a,8,9)
            merge_sort(a,8,8)
            merge_sort(a,9,9)
            merge(a,8,8,9)         a = 3 5 5 7 11 4 7 11 4 9 
            merge(a,5,7,9)         a = 3 5 5 7 11 4 4 7 9 11 
            merge(a,0,4,9)         a = 3 4 4 5 5 7 7 9 11 11 

    9    0    11    10    5     8    -7    6    8     7    5

            merge_sort(a,0,5)
            merge_sort(a,0,2)
            merge_sort(a,0,1)
            merge_sort(a,0,0)
            merge_sort(a,1,1)
            merge(a,0,0,1)    a = 0 9 11 10 5 8 -7 6 8 7 5 
            merge_sort(a,2,2)
            merge(a,0,1,2)    a = 0 9 11 10 5 8 -7 6 8 7 5 
            merge_sort(a,3,5)
            merge_sort(a,3,4)
            merge_sort(a,3,3)
            merge_sort(a,4,4)
            merge(a,3,3,4)    a = 0 9 11 5 10 8 -7 6 8 7 5 
            merge_sort(a,5,5)
            merge(a,3,4,5)    a = 0 9 11 5 8 10 -7 6 8 7 5 
            merge(a,0,2,5)    a = 0 5 8 9 10 11 -7 6 8 7 5 
            merge_sort(a,6,10)    
            merge_sort(a,6,8)
            merge_sort(a,6,7)
            merge_sort(a,6,6)
            merge_sort(a,7,7)
            merge(a,6,6,7)    a = 0 5 8 9 10 11 -7 6 8 7 5 
            merge_sort(a,8,8)
            merge(a,6,7,8)    a = 0 5 8 9 10 11 -7 6 8 7 5 
            merge_sort(a,9,10)
            merge_sort(a,9,9)
            merge_sort(a,10,10)
            merge(a,9,9,10)    a = 0 5 8 9 10 11 -7 6 8 5 7 
            merge(a,6,8,10)    a = 0 5 8 9 10 11 -7 5 6 7 8 
            merge(a,0,5,10)    a = -7 0 5 5 6 7 8 8 9 10 11