P82: refactor out INF and get-value
P82 refactor: tidy up fn
P82 refactor out two fns
P82 refactor: merge two fns into one
P82: refactor two fns into one
P82 refactor: remove 2 fns
P82: remove profiling
P82: solution in 4 minutes
Tidy up solution 82
P82: separate neighbour fn to allow passing of different rules
Solution 83
Solution 68 (slow)
P68: slight efficiency increase
P68 speed improvement
Solution 87