up to LPN exercise 6.5 [partially incomplete]

at e 6.5, my predicate is recursively obnoxious!
fixed LPN e6.5 & completed LPN e6.6
partial p6.2

first result to predicate yields answer + a "don't care" variable.
subsequent queries append an empty list + multiple "don't care"s
finished lpn 6
started lpn 7 & 4x4 sudoku
completed 4x4 sudoku
started CFGs
started Io track
Io track completely planned
Merge branch 'master' into prolog
first io steps
io/erl order rdm