This page describing the БЭСМ-6 instruction set refers to a value called ω, which is stored inside a Mode Register. It appears to be set by certain kinds of instructions, so that ω can tell you which of the last executed multiply and the last executed addition and the last executed subtraction was executed last. Kind of like how the Z80 has a bit that says whether an addition or subtraction happened last and is useful for the "decimal adjustment" operation.
Now the БЭСМ-6 has a Young Bits register1 and the precise semantics of fetching Young Bits into Accumulator depend on what's inside ω.
Now the БЭСМ-6 has a Branch if Zero instruction and correspondingly a Branch if Not Zero instruction, and the thing which determines what "Zero" is2 is some kind of calculation based on the value ω.
I'm finding this whole business kind of bizarre and hard to grok. So my question is basically "what's going on here?". Can you explain why Zero is not
0 and why this depends on ω and why loading Young Bits also depends on ω?
And bonus points also if you know the etymology. I have exactly no idea why this thing should be denoted by ω, the lower case omega.
1 Presumably, it's called Young Bits in this particular document because it's sometimes treated as an extension of the accumulator and the Russian word младший can mean "younger" and the same word also can mean "least significant" when talking about bits/bytes/digits, but I'm not aware that this use of the English word "younger" is in widespread use.
2 A hint: This Zero condition does not mean that Accumulator is numerically zero.