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Rather simple function returns curious result. Explanation requested.

• To: mathgroup at smc.vnet.net
• Subject: [mg131384] Rather simple function returns curious result. Explanation requested.
• From: James Stein <mathgroup at stein.org>
• Date: Tue, 2 Jul 2013 00:48:42 -0400 (EDT)
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• Delivered-to: l-mathgroup@wolfram.com
• Delivered-to: mathgroup-outx@smc.vnet.net
• Delivered-to: mathgroup-newsendx@smc.vnet.net

For reasons that escape me, the simple function below fails to return
an empty List when n==2; Is this a bug? If not, what is the
explanation? If the return value for n==2 is changed to an integer or
a string, the function behaves as expected.(Of course, this bizarre
function is the result of simplifying a more reasonable one.)

Clear[ f ];
f [run : { List___ } ] := Module [ { n },
   n = run // Length;
   If [ n != 2, Return [ n ] ];
   Module [ { } ,
    { } (* Return Empty List if n==2 *)
    ]
   ] ;
f [ { } ]
f [ { { } } ]
f [ { { }, { } } ]
f [ { { }, { }, { } } ]
f [ { { }, { }, { }, { } } ]

When I run the above, I get these four outputs:
0
1
Sequence[{}, {}][]
3
4

• Follow-Ups:
  • Re: Rather simple function returns curious result.
    • From: Bob Hanlon <hanlonr357@gmail.com>
  • Re: Rather simple function returns curious result. Explanation
    • From: Fred Simons <f.h.simons@tue.nl>