* @return {@code true} {@code true} if tensor u mathematically (not programming) equals to tensor v,
* {@code false} if they they differ only in the sign and {@code null} otherwise
*/
public static Boolean compare1(Tensor u, Tensor v) {
Indices freeIndices = u.getIndices().getFree();
if (!freeIndices.equalsRegardlessOrder(v.getIndices().getFree()))
return null;
int[] free = freeIndices.getAllIndices().copy();
IndexMappingBuffer tester = new IndexMappingBufferTester(free, false);
IndexMappingBuffer buffer = IndexMappings.createPortOfBuffers(tester, u, v).take();
if (buffer == null)