Question: How to obtain the new user-assigned names?

Suppose you do this

save something, afile.m;

and that later someone else does this

read afile.m;

Let's assume that this person does not know the names of the variables you have saved.
A way to get these names could be

before := { anames('user') };
read file.m:
after := anames('user') minus before minus {'before'}

I thought after would only contain something, but it also contains all the elements of before, just as if  
anames('user') minus before was not effective (see PS below)

Standard Worksheet Interface, Maple 2015.2, Mac OS X, December 

   21 2015 Build ID 1097895
before := {anames('user')};
after := {anames('user')} minus before minus {'before'}
                         {a, b}

How can I obtain the set of the new user-asigned names?

PS: Why does displaying  before give the value assigned to and not a itself?


Thanks in advance

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