Solutions by Bruce Gray.

For ch-2, the Perl and Raku programs can take rationals on the command-line for experimentation,
or will run their test suites if invoked without arguments.

Sample runs:
$ perl perl/ch-1.pl 
    104743

$ raku raku/ch-1.raku
    104743

$ perl perl/ch-2.pl 4817/5410
    4817/5410 has CW parent,grandparent of: 4817/593,4224/593

$ raku raku/ch-2.raku 4817/5410
    (4817/593 4224/593)

$ prove perl/ch-2.pl
    perl/ch-2.pl .. ok       
    All tests successful.
    Files=1, Tests=202,  0 wallclock secs ( 0.04 usr  0.01 sys +  0.09 cusr  0.01 csys =  0.15 CPU)
    Result: PASS

$ prove -e raku raku/ch-2.raku
    raku/ch-2.raku .. ok       
    All tests successful.
    Files=1, Tests=202,  3 wallclock secs ( 0.05 usr  0.00 sys +  2.72 cusr  0.13 csys =  2.90 CPU)
    Result: PASS

$ perl -MMath::PlanePath::RationalsTree -wE 'my $CW = Math::PlanePath::RationalsTree->new( tree_type => "CW" ); say join "/", $CW->n_to_xy( $CW->tree_n_parent( $CW->xy_to_n(@ARGV) ) );' 4817 5410
    4817/593
    (Fleshed out in ch-2_via_module.pl)