If you feel inspired by this kind of geometric stuff, check out The Geometry Junkyard for a huge collection of geometrical and recreational math.

@ARGV||push@ARGV,5;
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$}=1|1<<(pop||3);print($"x$},(map$_?'/\\':$"x2,
@;),$/),@;=(1,map$;[$_]^$;[-$_],1..@;)while$}--
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Nice one! I shaped your code like a triangle.

#!/usr/bin/perl
                     /\
                    /=~(
                   '(?{'.
                  ('`'|'%'
                 ).('['^'-'
                ).('`'|'!').
               ('`'|',').'"'.
              '\\$-=!\\$%|!\\'
             .'$%<<('.('['^'+')
            .('`'|'/').('['^'+')
           .'||'.('^'^('`'|'*')).
          ');'.('['^'+').('['^')')
         .('`'|')').('`'|'.').('['^
        '/').'(\\$\\"'.('['^'#').''.
       '\\$-,('.('`'|'-').('`'|'!').(
      '['^'+').'\\$_?'."'".'/\\\\\\\\'
     ."'".':\\$\\".\\$\\",\\@;),\\$/),'
    .'\\@;=(!\\$%,'.('`'|'-').('`'|'!').
   ('['^'+').'\\$;[\\$_]^\\$;[-\\$_],!\\'
  .'$%..\\@;)'.('['^',').('`'|'(').(('`')|
 ')').('`'|',').('`'|'%').'\\$---"})');'\+'
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Here is an alternative solution. This one is a little shorter and strict and warning safe. Also it does not emit an empty first line. I developed it from ideas in previous solutions posted to fwp@perl.org. See golf thread. If the alien golfers take up my challenge, it will be significantly shortened.

$_=$"x((1|1<<(pop||4))-1)."/\\
";print,s,(?<=\\)..,$&^"\017|",ge,s,$,/\\,while+s+^ ++
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Update: The golf dream team of Ton Hospel, Eugene van der Pijll, Mtv Europe and Keith C Ivey whittled 15 strokes from my initial offering:

#!perl -l
$_=$"x2**(pop||4);s'$'/\\',print,s/(?<=\\)../$&^aD^n8/egwhile+s\^ \\
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Here are some other solutions (without default argument) they concocted during their fidgeting:

$_=$"x(1<<pop);print,s/(?<=\\)../$&^"\17|"/egwhile+s^\n?$^/\\\n^,s\^ \
+\
$_=$"x(1<<pop).$/;print,s/(?<=\\)../$&^"\17|"/egwhile+s^$^/\\^,s\^ \\
-lX $_=$"x2**pop;print,s/(?<=\\)../$&^"\17|"/egwhile+s*$*/\\**s+^ ++
-lX $_=$"x2**pop;print,s/(?<=\\)../$&^"\17|"/egwhile+s-^ (.*)-$+/\\-
-l $_=$"x2**pop;s'$'/\\',print,s/(?<=\\)../$&^"\17|"/egwhile+s\^ \\
-l $_=$"x2**pop;s'$'/\\',print,s/(?<=\\)../$&^aD^n8/egwhile+s\^ \\
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Still going! Though not shortest, I find this one amusing for some reason. Oh, and I have given it a name: "five substitutions".

#!perl -l
s--$"x$^F**pop-e,s-.-s,,,,s,$,/\\,,print,s,(?<=/.)..,$&^h9^gE,ge-ge
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