How to build a static library for both iPhone OS 3 and OS 4?

I created a .a lib file and it was built under iPhone OS 3.0 (in XCode 3.2.2). Now I found that it doesn't work on OS 4. I was using the lipo command to build the .a file for both simulator version and device version:

lipo -cre开发者_如何转开发ate libdevice.a libsimulator.a -output libcombined.a

Now I created another .a file under iPhone OS 4.0 (in XCode 3.2.3). My question is that is it possible to combine the two lib files together? (libcombined3.a and libcombined4.a)

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the 4.0 version will work on 3.0, you don't need the 3.0 specific version anymore. Move completely over to iOS4.