[Illustration:
+-----------------+
| C E |
| | | |
| D F |
+---------------B |
G |
A | |
| H |
+-----------------+
]
As the conditions are generally understood, this puzzle is incapable of
solution. This can be demonstrated quite easily. So we have to look for
some catch or quibble in the statement of what we are asked to do. Now
if you fold the paper and then push the point of your pencil down
between the fold, you can with one stroke make the two lines CD and EF
in our diagram. Then start at A, and describe the line ending at B.
Finally put in the last line GH, and the thing is done strictly within
the conditions, since folding the paper is not actually forbidden. Of
course the lines are here left unjoined for the purpose of clearness.
In the rubbing out form of the puzzle, first rub out A to B with a
single finger in one stroke. Then rub out the line GH with one finger.
Finally, rub out the remaining two vertical lines with two fingers at
once! That is the old trick.