#! perl -slw
use strict;
use List::Util qw[ first ];

sub leftSubset{
    local $^W;
    my( $major, $minor) = @_;
    return @{$minor} == first{
        $major->[ $_ ] ne $minor->[$_]
    } 0 .. @{$minor}
}

my @a = 'a' .. 'f';

print "\n@$_\n is left subset of \n@a: ",
    leftSubset( \@a, $_ ) ? 'YES' : 'NO'
    for ['a'..'c'], ['b'..'d'],[qw[a a b c]],[ reverse 'a'..'c'];;

__END__
P:\test>junk2

a b c
 is left subset of
a b c d e f: YES

b c d
 is left subset of
a b c d e f: NO

a a b c
 is left subset of
a b c d e f: NO

c b a
 is left subset of
a b c d e f: NO