Overhaul: uu0 split into uu0a, uu0b, uu0c, and uu0d.

1. I have reverted to the uu0 from 0a09536 to resolve the slowdown issue. 

2. The uu0 where the use of match was completely eliminated is preserved in uu0_no_use_of_match.

3. The substantially new material from uu0_no_use_of_match is added to uu0 (this includes the two-out-of-six property for the weak equivalences.

4. uu0 is split into four parts.

5. . New material was added to Current_work in particular the file sSet with a complete definition of the category of simplicial sets that compiles.