Array concatenation (from David Fanning)

This time quoting from http://www.dfanning.com/tips/array_concatenation.html

a=make_array(4,4,VALUE=1b)
help,a                          ;A               BYTE      = Array[4, 4]
b=make_array(4,4,VALUE=2b)
help,b                          ;B               BYTE      = Array[4, 4]
help,[a,b]                      ;<Expression>    BYTE      = Array[8, 4]
help,[[a],[b]]                  ;<Expression>    BYTE      = Array[4, 8]
help,[[[a]],[[b]]]              ;<Expression>    BYTE      = Array[4, 4, 2]