SWITCH SWITCH A device for making, breaking, or changing the connec- tions in an electric circuit. SYMBOLIC LOGIC The discipline in which valid arguments and operations are dealt with using an artificial language designed to avoid the ambiguities and logical inadequacies of natural lan- guages. SYMMETRICAL LAMINATE A composite laminate in which the sequence of plies below the laminate midplane is a mirror image of the stacking sequence above the midplane. SYMMETRICALLY OPPOSITE PARTS Symmetrically oppo- site parts are those parts that are mirror images of each other. SYMMETRICAL PAIR A balanced transmission line in a multi- pair cable having equal conductor resistances per unit length, equal impedances from each conductor to earth, and equal impedances to other lines. SYSTEM (Electrical-Electronic) A combination of two or more sets, which may be physically separated when in operation, and such other assemblies, subassemblies, and parts necessary to per-