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 foreach key
  foreach dependency of that key
   if this dependency is the one I want to delete, delete this key
  continue looping
 continue looping

  if( grep { $_ eq $key } @{$dependencies{$key}} ) {
    print "Going to call sub for $key\n";
    mydel($key);
  }

my %requiredby;
for my $key (keys $dependencies) {
...
for my $key (keys %dependencies) {
    push @{$requiredby{$_}}, $key for @{$dependencies{$key}};
}

#!/usr/bin/env perl5

...


my_del('one');

% ./tst.pl 
Going to call sub for four
...
Deleting three
Deleting four
Deleting one