Therefore, (12-U 1)/3 is the current of 3 Ω resistance, which is positively related to the voltage (from left to right), so it is the current flowing into the node 1.
U 1/4 is 4 Ω resistance current, which keeps positive direction (upper positive and lower negative) when it is associated with u 1, so it is the current flowing from node1;
Similarly, (U 1-U6-U2)/2 is a current with a resistance of 2 Ω, which is consistent with (U 1-6) and flows out of the node 1 from left to right.
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