Barry Monson asks

I wish to find the normalizer of a subset T of a group G,
where T need not be a subgroup. For example, say

G:= Group(a,b,c,d); # a,b,c,d permutations,say

     T:= [a,d];                 # a subset of the generating set
                                # -- perhaps not quite a legitimate
                                # data structure,
                                # but you get the idea
Note that T is not the subgroup generated by a,d . Nevertheless, I want

N:= Normalizer in G of T

How do I proceed? My apologies if I have missed something obvious
in the documentation. Thanks for your advice.

One possibility is to use

T := Set(T);
Stabilizer(G,T,OnSets);

Steve