Classical unified field theories since antisymmetry seemed essential for electromagnetism, the symmetry requirement was relaxed for one or both fields. Einstein's proposed unified-field equations (fundamental laws of physics) were generally derived from a variational principle expressed in terms of the Riemann curvature tensor for the presumed space-time manifold. In field theories of this kind, particles appear as limited regions in space-time in which the field strength or the energy density are particularly high. Einstein and coworker Leopold Infeld managed to demonstrate that, in Einstein's final theory of the unified field, true singularities of the field did have trajectories resembling point particles. However, singularities are
Unified combatant command the space-related responsibilities previously assigned to the Commander, United States Strategic Command; and (3) the responsibilities of Joint Force Provider and Joint Force Trainer for Space Operations Forces". A sub-unified command, or, subordinate unified command, may be established by combatant commanders when authorized to do so by the Secretary of Defense or the president. They are created to conduct a portion of the mission or tasking of their parent geographic or functional command. Sub-unified commands may be either functional or geographic, and the commanders of sub-unified commands exercise authority similar to that of combatant commanders. Examples of current and former