    # File lib/standard/facets/math/epsilon.rb, line 7
      def self.epsilon(i, j, k)
        i = Integer(i)
        return nil if i < 1 or i > 3
        j = Integer(j)
        return nil if j < 1 or j > 3
        k = Integer(k)
        return nil if k < 1 or k > 3
        case i * 16 + j * 4 + k
          when 27, 45, 54 then return  1
          when 30, 39, 57 then return -1
        end
        0
      end