Typical applications, Three- (or more) terminal devices: Thyristor, reverse-blocking triode-type, P-type gate; semiconductor controlled rectifier, P-type gate - General.
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(in English) (1993)  315-1975 - IEEE Standard American National Standard Canadian Standard Graphic Symbols for Electrical and Electronics Diagrams (Including Reference Designation Letters), IEEE, p. 128  DOI:  10.1109/IEEESTD.1993.93397. ISBN:  0738109479.
Michel Bakni