Three level logical circuits

Claim 1

A LOGICAL BLOCK COMPRISING, A CONSTANT CURRENT SOURCE, FIRST, SECOND AND THIRD TRANSISTORS, EEACH HAVING EMITTER, BASE AND COLLECTOR ELEMENTS, MEANS CONNECTING ALL OF SAID EMITTERS TO SAID CONSTANT CURRENT SOURCE, MEANS FOR APPLYING AN INPUT SIGNAL TO THE BASE OF SAID FIRST TRANSISTOR, SAID INPUT SIGNAL VARYING BETWEEN A FIRST VOLTAGE LEVEL AT WHICH SAID TRANSISTOR IS NON-CONDUCTING AND A SECOND VOLTAGE LEVEL AT WHICH SAID TRANSISTOR IS CONDUCTING, MEANS FOR APPLYING AN INPUT SIGNAL TO THE BASE OF SAID SECOND TRANSISTOR, SAID SIGNAL VARYING BETWEEN SAID FIRST VOLTAGE LEVEL AT WHICH SAID SECOND TRANSISTOR IS CUT OFF AND A THIRD VOLTAGE LEVEL WHICH TENDS TO RENDER SAID TRANSISTOR MORE CONDUCTIVE THAN SAID SECOND VOLTAGE LEVEL, MEANS COUPLING THE BASE OF SAID THIRD TRANSISTOR TO A FIXED VOLTAGE LEVEL AT WHICH SAID THIRD TRANSISTOR WILL BE RENDERED CONDUCTIVE WHEN BOTH SAID FIRST AND SECOND TRANSISTORS ARE RENDERED NON-CONDUCTIVE, AND MEANS TO DERIVE AN OUTPUT FROM SAID FIRST AND THIRD TRANSISTORS.