Oracle libraries : libcore.a vs libcore3.a

I was wondering if anyone could tell me the difference between some libraries. Our software builds on different platforms and sometimes certain library names don't work. What does that "3" stand for:

	libcore.a    vs   libcore3.a
	libnlsrtl.a  vs	  libnlsrtl3.a
	libcv6.a     vs	  libc3v6.a

Thanks,
Ken

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