Maxima Function
first (expr)
Returns the first part of expr which may result in the first
element of a list, the first row of a matrix, the first term of a sum,
etc. Note that first and its related functions, rest and last, work
on the form of expr which is displayed not the form which is typed on
input. If the variable inflag is set to true however, these
functions will look at the internal form of expr. Note that the
simplifier re-orders expressions. Thus first(x+y) will be x if inflag
is true and y if inflag is false (first(y+x) gives the same
results). The functions second .. tenth yield the second through the
tenth part of their input argument.