I'm not sure that 'leftSubset' is the best name, but it should work for any type of values. Though, if you want '2' to compare equal to '2.0', you'll need to tweak it.

It takes a references to the two arrays, the master first, the variable array second, and returns true false.

#! 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
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