Too much abstract freedom? N adjacent tree nodes, N neighbouring states, etc.

Hm. I'm not convinced by that argument.

1. map is a piece of paper with colored lines and symbols; or the process of making one.
2. reduce, is what you do to a good sauce or damaged goods.

I think context and convention; along with conciseness and memorability are key here.

For each element, one property is defined: the successor.

Hm. Can you have a successor without a predecessor? And actually, this deals with both -- or potentially more:

sub mapAdj(&$@) {
    local( $a, $b, $c, $d, $e, $f, $g, $h, $i, $j );
    my( $code, $n ) = ( shift, shift );
    map $code->(
        ($a, $b, $c, $d, $e, $f, $g, $h, $i, $j ) = @_[ $_-$n .. $_ ]
    ), --$n .. $#_;
}

my @accum = mapAdj{ $a + $b + $c } 3, 1..10;
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And 'successor' tends to have mathematical connotations which don't apply to a list of *any*things.

For the simple case of adjacent pairs, I toyed with forByTwo() :)