Very nice, but your logic is reversed.  Remember, an isogram does NOT have any letters duplicated.

To keep it golfed, either change the caller of the subroutine: 

print "$_ is ", (isogram() ? 'not ' : ''), "an isogram\n" for @ARGV;

[download]

or, better yet, the subroutine name: 

sub not_isogram {
    # ...
}
print "$_ is ", (not_isogram() ? '': 'not '), "an isogram\n" for @ARGV
+;

[download]
s''(q.S:$/9=(T1';s;(..)(..);$..=substr+crypt($1,$2),2,3;eg;print$..$/

In reply to Re^3: testing number of occurrences in a word by liverpole
in thread testing number of occurrences in a word by jsmith

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