I think itīs well-known the challenge of connecting 9 dots forming a 3x3 array, with 4 straight lines without lifting the pencil from the paper:

            *     *     *

            *     *     *

            *     *     *

But, what about these two where the lines must form a closed loop:

1) Connect the 12 dots with 5 straight lines:

         *     *     *     *

         *     *     *     *

         *     *     *     *

2) Connect the 16 dots with 6 straight lines:

          *     *     *     *

          *     *     *     *

          *     *     *     *

          *     *     *     *

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