$ cat >> $HGRCPATH <<EOF

  > [extensions]

  > drawdag=$TESTDIR/drawdag.py

  > bruterebase=$TESTDIR/bruterebase.py

  > [experimental]

  > evolution.createmarkers=True

  > evolution.allowunstable=True

  > EOF

  $ init() {

  >   N=`expr ${N:-0} + 1`

  >   cd $TESTTMP && hg init repo$N && cd repo$N

  >   hg debugdrawdag

  > }

Source looks like "N"

  $ init <<'EOS'

  > C D

  > |\|

  > A B Z

  > EOS

  $ hg debugbruterebase 'all()-Z' Z

     A: A':Z

     B: B':Z

    AB: A':Z B':Z

     C: ABORT: cannot rebase 3:a35c07e8a2a4 without moving at least one of its parents

    AC: A':Z C':A'B

    BC: B':Z C':B'A

   ABC: A':Z B':Z C':A'B'

     D: D':Z

    AD: A':Z D':Z

    BD: B':Z D':B'

   ABD: A':Z B':Z D':B'

    CD: ABORT: cannot rebase 3:a35c07e8a2a4 without moving at least one of its parents

   ACD: A':Z C':A'B D':Z

   BCD: B':Z C':B'A D':B'

  ABCD: A':Z B':Z C':A'B' D':B'

Moving backwards

  $ init <<'EOS'

  > C

  > |\

  > A B

  > |

  > Z

  > EOS

  $ hg debugbruterebase 'all()-Z' Z

    B: B':Z

    A: 

   BA: B':Z

    C: ABORT: cannot rebase 3:b8d7149b562b without moving at least one of its parents

   BC: B':Z C':B'A

   AC: 

  BAC: B':Z C':B'A