adjacency = (a,b) ->
    if a>b
        adjacency b, a
    else
        false if a is b
        switch b
            when 2 then (a is 1)
            when 3 then (a is 2)
            when 4 then (a in [1,2])
            when 5 then (a in [1..4])
            when 6 then (a in [2,3,5])
            when 7 then (a in [4,5])
            when 8 then (a in [4..7])
            when 9 then (a in [5,6,8])
            else false