Test "cast off 3/4" and variants, ensuring that it works from 3-and-1 lines
and that the "center pushes the end".

sdr> heads lead right ; veer left
| 4B>  1B>
| 
| 4G>  1G>
| 
| 3G<  2G<
| 
| 3B<  2B<
sdr> /// here all ends are beaus
sdr> cast off 3/4
| 4Gv  4Bv  1Gv  1Bv
| 
| 3B^  3G^  2B^  2G^
sdr> /// but now some ends are belles
sdr> cast off 3/4
| 4B>  1G<
| 
| 4G>  1B<
| 
| 3B>  2G<
| 
| 3G>  2B<
sdr> /reset
sdr> /// now test 3-and-1 lines
sdr> heads lead right ; veer left
| 4B>  1B>
| 
| 4G>  1G>
| 
| 3G<  2G<
| 
| 3B<  2B<
sdr> side boys run
| 4G>  1B>
| 
| 4B<  1G>
| 
| 3G<  2B>
| 
| 3B<  2G<
sdr> /// beaus are ends
sdr> cast off 3/4
| 4G^  4Bv  1Gv  1Bv
| 
| 3B^  3G^  2B^  2Gv
sdr> u-turn back
| 4Gv  4B^  1G^  1B^
| 
| 3Bv  3Gv  2Bv  2G^
sdr> /// belles are ends
sdr> cast off 3/4
| 4G<  1B<
| 
| 4B>  1G<
| 
| 3G>  2B<
| 
| 3B>  2G>
sdr> /reset
sdr> /// finally, test a cast 3/4 which should be illegal
sdr> heads touch 1/4
| 4B>  1B>  1G>  2G<
| 
| 4G>  3G<  3B<  2B<
sdr> cast off 3/4
* Need to be in miniwave or line of 4.
sdr> /exit