n=->(s){q=(0...s);p=q.to_a.permutation;p.reject{|b|(0..s-2).any?{|o|q.any?{|t|t>o&&(t-o).abs==(b[t]-b[o]).abs}}}}
Replying to @ElementOfPage
@ElementOfPage things.select{|a|a.exists?}.each{|b|b.destroy}
7:39 PM - 23 Jan 2015
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