Structure of an Mlist tree:

--- p.answer pointers

|   along members of the same array
The end of the array is a structure with p.mv & MV_LAST being nonzero.

0-9: Depth number (0 is root node)
A:   Side to move first
B:   Side to move second
a-z: Alternate moves with same move number

For possible mate in 1
0---1Aa
    |
    1Ab
    |
    1Ac

Printed for white to move first as
1. a
1. b
1. c

Printed for black to move first as
1. ... a
1. ... b
1. ... c

For impossible mate in 1
0---1Aa---2Bd
    |     |
    |     2Be
    |
    1Ab---2Bf
    |
    1Ac---2Bg
          |
          2Bh

Printed for white to move first as
1. a d
     e
1. b f
1. c g
     h
 
Printed for black to move first as
1. ... a 2. d
            e
1. ... b 2. f
1. ... c 2. g
            h


For possible mate in 2
0---1Aa---2Bd---3Ae
    |     |
    |     2Bf---3Ag
    |
    1Ab---2Bh---3Ai
    |
    1Ac---2Bj---3Ak
          |
          2Bl---3Am

Printed for white as
1. a d 2. e
     f 2. g
1. b h 2. i
1. c j 2. k
     l 2. m