-- -*- M2-comint -*- {* hash: 442719131 *}

i1 : D4 = typeD(4)

o1 = {x  - x , x  + x , x  - x , x  + x , x  - x , x  + x , x  - x , x  + x , x  - x , x  + x , x  - x , x  + x }
       1    2   1    2   1    3   1    3   1    4   1    4   2    3   2    3   2    4   2    4   3    4   3    4

o1 : Hyperplane Arrangement 

i2 : describe D4

o2 = {x  - x , x  + x , x  - x , x  + x , x  - x , x  + x , x  - x , x  + x ,
       1    2   1    2   1    3   1    3   1    4   1    4   2    3   2    3 
     ------------------------------------------------------------------------
     x  - x , x  + x , x  - x , x  + x }
      2    4   2    4   3    4   3    4

i3 : ring D4

o3 = QQ[x , x , x , x ]
         1   2   3   4

o3 : PolynomialRing

i4 :