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Mathematica Collect function

• To: mathgroup at smc.vnet.net
• Subject: [mg110680] Mathematica Collect function
• From: Minh <dminhle at gmail.com>
• Date: Fri, 2 Jul 2010 02:55:23 -0400 (EDT)

Given that:
Expand[((1 + Sqrt[2]) i - 1)/4*(P10 - P11) - (1 + Sqrt[2] + i)/
   4*(P20 - P21)]

will output
-(P10/4) + (i P10)/4 + (i P10)/(2 Sqrt[2]) + P11/4 - (i P11)/4 - (
 i P11)/(2 Sqrt[2]) - P20/4 - P20/(2 Sqrt[2]) - (
 i P20)/4 + P21/4 + P21/(2 Sqrt[2]) + (i P21)/4

How do I get from:
-(P10/4) + (i P10)/4 + (i P10)/(2 Sqrt[2]) + P11/4 - (i P11)/4 - (
 i P11)/(2 Sqrt[2]) - P20/4 - P20/(2 Sqrt[2]) - (
 i P20)/4 + P21/4 + P21/(2 Sqrt[2]) + (i P21)/4

back to
((1 + Sqrt[2]) i - 1)/4*(P10 - P11) - (1 + Sqrt[2] + i)/
   4*(P20 - P21)

I've tried using the Collect function as follows:
Collect[-(P10/4) + (i P10)/4 + (i P10)/(2 Sqrt[2]) + P11/4 - (i P11)/
  4 - (i P11)/(2 Sqrt[2]) - P20/4 - P20/(2 Sqrt[2]) - (i P20)/4 + P21/
  4 + P21/(2 Sqrt[2]) + (i P21)/4, {(P10 - P11), (P20 - P21)}]
but it doesn't seem to collect the terms {(P10 - P11), (P20 - P21)}.

Got any suggestions?