# File lib/more/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