Option variable
inflagDefault value: false
When inflag is true, functions for part
extraction inspect the internal form of expr.
Note that the simplifier re-orders expressions.
Thus first (x + y) returns x if inflag
is true and y if inflag is false.
(first (y + x) gives the same results.)
Also, setting inflag to true and calling part or substpart is
the same as calling inpart or substinpart.
Functions affected by the setting of inflag are:
part, substpart, first, rest, last, length,
the for ... in construct,
map, fullmap, maplist, reveal and pickapart.