minor change to make it work with coq trunk patched

For some strange reason, the use of "abstract" caused coq
to go into never-never land at the end of the file.
now works with coq trunk patched

coq version:
    	    https://github.com/DanGrayson/coq/commit/f23efe49ae9a806f5a510448897935e9ac56445b

Foundations version:
	    https://github.com/DanGrayson/Foundations2/commit/8908b92887f7704d5f9c946d5930fdec8358a472