1. A compoud buffer inverter for use in an integrated circuit that employs a single power supply connectible between first and second supply rails and that is particularly adapted for operation at low power supply voltages, said compound buffer inverter being operative to provide substantial current gain with a single signal polarity inversion and level shifting capability, said compound buffer inverter comprising: a first transistor having its emitter coupled to said first rail, its collector providing a current output terminal capable of assuming a potential between said first and second rails and a base; a second transistor complementary of said first transistor, said second transistor having a collector coupled to said first rail, an emitter coupled to said base of first transistor, and a base coupled to a circuit input terminal; current supply means coupled between said base of said first transistor and said second rail; means for operating said first transistor such that its emitter base potential is equal to or greater than the emitter base potential of said second transistor; and means for boosting the bias current to said first and second transistors with increasing load current.