use v5.10.0;
{ package C1; sub c1 { } our @ISA = qw(C2) }
{ package C2; sub c2 { } our @ISA = qw(C3) }
{ package C3; sub c3 { } our @ISA = qw(  ) }
{ package C4; sub c4 { } our @ISA = qw(  ) }
{ package C5; sub c5 { } our @ISA = qw(C1 C4) }
my $obj = bless {}, 'C5';
$main::global = bless {}, 'C5';
$DB::single = 1;
say "Done.";