Input from Prolog streams that have opened
the user's terminal for reading is echoed back as output to the same
terminal.
This is interleaved with output from other
Prolog streams that have opened the user's terminal for writing.
Therefore, all streams connected to the user's terminal share
the same set of position
counts and thus return the same values for each of the
predicates
character_count/2, line_count/2 and
line_position/2.