Using GAP to find the left coset of a subgroup. What am I doing wrong?

Question

If $g=(1,2,3)\in A_4$ then to find the right coset $Hg$ of the subgroup $H=\langle(1, 2)(3, 4)\rangle=\{(), (1,2)(3,4)\}$ in $A_4$, we just need to run the code:

gap> a4:=AlternatingGroup(4);
Alt( [ 1 .. 4 ] )
gap> H:=Subgroup(a4, [(1,2)(3,4)]);
Group([ (1,2)(3,4) ])
gap> g:=(1,2,3);
(1,2,3)
gap> R:=RightCoset(H,g);
RightCoset(Group([ (1,2)(3,4) ]),(1,2,3))
gap> Elements(R);
[ (1,2,3), (1,3,4) ]

However, repeating the same procedure for the left coset $gH$ returns the following error:

gap> L:=LeftCoset(H,g);
Error, Variable: 'LeftCoset' must have a value

Can someone please help me in understanding the following two things:

1) What does the error mean when finding the left coset $gH$?

2) Why is GAP calling the set $\{(1,2,3), (1,3,4)\}$ a right coset, when this is in fact the left coset $gH$ if you do the calculations by hand?

Thank you for your help.

EDIT: I am running GAP version 4.11.0, which is the latest version I think.

EDIT: @DerekHolt solved the problem for me:

gap> g1:=(1,3,2);
(1,3,2)
gap> L:=RightCoset(H,g1);
RightCoset(Group([ (1,2)(3,4) ]),(1,3,2))
gap> Elements(L);
[ (2,3,4), (1,3,2) ]

So that the left coset would be $\{(2,4,3), (1,2,3)\}$ (I wonder if this last step can be automated?).

Answer 1

@DerekHolt solved the problem for me:

gap> g1:=(1,3,2);
(1,3,2)
gap> L:=RightCoset(H,g1);
RightCoset(Group([ (1,2)(3,4) ]),(1,3,2))
gap> Elements(L);
[ (2,3,4), (1,3,2) ]

So that the left coset would be $\{(2,4,3), (1,2,3)\}$.