The graph of y^4 - 4x^4 = 2y^2 - 1 is the union of the graphs of two different conic sections. Which two types of conic sections are they?
(Write your answer as a list, with "C" for circle, "E" for ellipse, "H" for hyperbola, and "P" for parabola. For example, "C, H" if you think the graph consists of a circle and a hyperbola. You may use a letter twice.)