I assume the ternary weight’s memory representation requires two bits, so why do they use only three values instead of four? OTOH, I’m not sure what fourth valu

I assume the ternary weight’s memory representation requires two bits, so why do they use only three values instead of four? OTOH, I’m not sure what fourth value would useful for LLM models doing math with -1, 0, and 1. Infinity? NaN?