first
l
first
returns the first element of a non-
empty list:
l
first([3, 5, 7, 11, 13])
==>
3
l
first([[3, 5, 7], 11, 13])
==>
[3, 5, 7]
l
first([ ]) doesnŐt make sense; it returns an
error value
l
Be sure that the argument to first is not
[].