use strict;
use warnings;
{package Foo; sub m1; sub m2 {} our @a; }
{package Bar; our @ISA = 'Foo'; }
print(find_implementor('Bar', 'm1' ) // "[undef]", "\n");  # Foo
print(find_implementor('Bar', 'm2' ) // "[undef]", "\n");  # Foo
print(find_implementor('Bar', 'a'  ) // "[undef]", "\n");  # [undef]
print(find_implementor('Bar', 'isa') // "[undef]", "\n");  # UNIVERSAL