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Question: Determine numelems for an unassigned variable

Question:Determine numelems for an unassigned variable

smith_alpha 155
assign unassign
September 26 2015
1

Suppose I have a table of variables

 

f[1]:=a;

f[2]:=b;

 

numelems(f); gives 2.

 

In case I have not assign f, 

unassign(f);
numelems(f); gives error message.

 

Is there any simple way let maple detect that if it is unassined, numelems(f), can provide zero?

 

Thank you very much

 
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