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If the left transistor (T1) is close the output A1 has high level "1".
Through the base resistor (18kΩ) the left transistor (T2) is hold open, because A1 is "1" and T2 gets positive base voltage. So the output A2 has low level "0". Through the base resistor of T1 the base is hold on low level and hold the transistor close.
If you put the input E20 to ground or give a negative pulse, T2 close and A2 changes to "1". At the same time the base of T1 gets also high level from the base resistor. A1 changes to "0". Now the base of T2 is hold on low level by A1. After the input E20 is not more grounded or the negative pulse is gone, this condition is hold until E10 is grounded or gets a negative pulse.
The conditions at the outputs changes, when a negative pulse arrive at the opposite input.