CopyListEntries can create lists when the last element is unbound

[ChrisJefferson]

In GAP, lists should always have a bound last element, but CopyListEntries can be used to create a completely unbound list, for example:

gap> l := [1,2,3,4,5,6];
[ 1, 2, 3, 4, 5, 6 ]
gap> CopyListEntries([], 1, 1, l, 1, 1, 6);
gap> l;
[ ,,,,, ]

This list is very "fragile", for example:

gap> IsBound(l[6]);
false
gap> l;
[ ,,,,, ]
gap> Length(l);
6
gap> Unbind(l[6]);
gap> l;
[  ]

[fingolfin]

Nice catch. Exists since GAP 4.5; in GAP 4.4, the input above results in an error:

List Elements: [1] must have an assigned value