insert_cell_0_in_cell_1 ( CMap& cm, typename CMap::Dart_handle dh)
Inserts a 0-cell in the 1-cell containing dh.
Returns a handle on one dart belonging to the new 0-cell.
Precondition:
CMap::dimension≥1 and *dh∈cm.darts().
See example in Figure 27.11.
If 1-attributes are non void,
Attribute_type<1>::type::On_split(a,a') is called, with a the original 1-attribute associated
with dh and a' the new 1-attribute created during the operation.