Conway's Game of Life in J

I thought I'd give J (link) a try and implemented Conway's Game of Life in it.

Code: 
step =: ((]+.&(3&=)+)(+/@(((4&{.,(_4&{.))(>,{,~<i:1))&|.)))~

Sample: 
   step =: ((]+.&(3&=)+)(+/@(((4&{.,(_4&{.))(>,{,~<i:1))&|.)))~
   [ f =: 5 5 $ 0 1 0 0 0   0 0 1 0 0   1 1 1 0 0   0 0 0 0 0    0 0 0 0 0
0 1 0 0 0
0 0 1 0 0
1 1 1 0 0
0 0 0 0 0
0 0 0 0 0
   step f
0 0 0 0 0
1 0 1 0 0
0 1 1 0 0
0 1 0 0 0
0 0 0 0 0
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