Use of erf(x); read text file; command to display available functions



Why doesn't erf(5) produce a numerical result, whereas sin(.3) or
gamma(.2) do?
 
I am using Maxima 5.12.0.
 
It appears that my version is not finding a definition for erf.
 
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Can Maxima read a text file containing a column of numbers?
 
 
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Is there a function to display available functions - not just those
defined by a user?
 
 
 
 
Thanks.