ag-gipp/GoUldI

<math xmlns='http://www.w3.org/1998/Math/MathML' display='inline'><semantics><mrow><mo stretchy="false">(</mo><mi>x</mi><mo>−</mo><mi>y</mi><msup><mo stretchy="false">)</mo> <mn>2</mn></msup><mi>U</mi><mo>=</mo><msup><mrow><mo>(</mo><msqrt><mrow><msup><mi>x</mi> <mn>4</mn></msup><mo>+</mo><msup><mi>a</mi> <mn>4</mn></msup></mrow></msqrt><mo>+</mo><msqrt><mrow><msup><mi>y</mi> <mn>4</mn></msup><mo>+</mo><msup><mi>a</mi> <mn>4</mn></msup></mrow></msqrt><mo>)</mo></mrow> <mn>2</mn></msup><mo>−</mo><mo stretchy="false">(</mo><msup><mi>x</mi> <mn>2</mn></msup><mo>−</mo><msup><mi>y</mi> <mn>2</mn></msup><msup><mo stretchy="false">)</mo> <mn>2</mn></msup></mrow><annotation encoding='application/x-tex'>(x-y)^{2}U=\left(\sqrt{x^{4}+a^{4}}+\sqrt{y^{4}+a^{4}}\right)^{2}-(x^{2}-y^{2})^{2}</annotation></semantics></math>