Ah, got it. I think my conceptual problem was that I don't think I ever use (or think of) references as a way to set the referenced variable's value. A reference to me tends to mean that either I need a complex data-structure, or I've got a fussy return from a subroutine (e.g. two separate variable-length lists that I need to keep separate).

Anyway, many thanks your holiness.

map{$a=1-$_/10;map{$d=$a;$e=$b=$_/20-2;map{($d,$e)=(2*$d*$e+$a,$e**2
-$d**2+$b);$c=$d**2+$e**2>4?$d=8:_}1..50;print$c}0..59;print$/}0..20
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