dd_C doesn't work in Complexes

[mahrud]

I had mentioned this bug about the cohomological notation for getting the differentials of a complex in an email, but mentioning it again here. cc @ggsmith

i1 : R = kk[x,y]

o1 = R

o1 : PolynomialRing

i2 : C = koszulComplex vars R

      1      2      1
o2 = R  <-- R  <-- R

     0      1      2

o2 : Complex

dd^C works fine:

i3 : dd^C

          1               2
o3 = 0 : R  <----------- R  : 1
               | x y |

          2                  1
     1 : R  <-------------- R  : 2
               {1} | -y |
               {1} | x  |

o3 : ComplexMap

But dd_C, which is explicitly mentioned in the documentation, does not work:

i4 : dd_C

o4 = dd
        1      2      1
       R  <-- R  <-- R

       0      1      2

o4 : IndexedVariable

[mikestillman]

We remove dd_C from the documentation, instead of allowing it.

[mahrud]

Reopening until #4395 is merged.