Tests for peel the top from Z formations.

sdr> heads lead right ; extend
| 4B>  1B>
| 
| 3G<  2G<
| 
| 4G>  1G>
| 
| 3B<  2B<
sdr> ends fold
|      3G<  4B<       2G<  1B<
|
| 3B>  4G>       2B>  1G>
sdr> peel the top
| 4G^  3Bv  4B^  3Gv  1G^  2Bv  1B^  2Gv
sdr> ends fold
| 4Gv       1Gv
| 
| 3Bv  4B^  2Bv  1B^
| 
|      3G^       2G^
sdr> peel the top
| 3B>  2B>
| 
| 4G<  1G<
| 
| 3G>  2G>
| 
| 4B<  1B<
sdr> /exit