Here is what I mean by commified. Consider the following 2 versions of the same map statement:

...map{"@$_\n"}@a...
...map"@$_\n",@a...
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The first form is more general, you can put more complex logic inside the block. The second form replaces the block with a comma and shaves a character. Often you can shave a few characters off of someone's solution by seeing that a few map's or grep's can switch over to the version with the comma.

Sometimes it is not obvious that you can. So sometimes I just have to try it out. As in the case:

...map{$$_[0]>$i?():[$i,@$_]}P($n-$i)...
...map$$_[0]>$i?():[$i,@$_],P($n-$i)...
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Incidentally the following version is the same size, but has slightly nicer (IMHO) output:

sub P{
my$i=pop;[$i],map{--$i;map$$_[0]>$i?():[$i,@$_],P($_-1)}2..$i
}
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