direction of flow of electric current in a circuit
Electric current Since the current in a wire or component can flow in either direction, when a variable I is defined to represent that current, the direction representing positive current must be specified, usually by an arrow on the circuit schematic diagram. This is called the reference direction of current I. If the current flows in the opposite direction, the variable I has a negative value.
Alonso Álvarez de Pineda
Exponentiation Any nonzero number raised to the 0 power is 1:[11]
Z-transform The Z-transform can be defined as either a one-sided or two-sided transform.[7]