Projection of other observation #638

Job	Run time
Unit tests (ubuntu-20.04, 3.7)	16m 11s
conda install latest tensorflow (ubuntu-20.04)	4m 16s
conda install (ubuntu-20.04)	2m 37s
Build documentation	2m 12s
Unit tests (macos-11, 3.7)	39m 34s
Test uproot3 (ubuntu-20.04, 3.7)	16m 19s
Style checks	2m 25s
Unit tests (ubuntu-20.04, 3.6)	15m 25s
Unit tests (ubuntu-20.04, 3.8)	15m 12s
Coverage (ubuntu-20.04, 3.7)	17s
	1h 54m 28s

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