One gotcha here if you're not expecting it is that package subroutines set $_[0] to the value on the left-side of ->. So, for example, the following returns 'FP', not 'Hello':

print FP->subtest1('Hello');
package FP;{sub subtest1{return shift;}}
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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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