This one-row-from-network lesson treats a truth-table entry as a physical switch-network case before it becomes a table cell. For the stated HIGH/HIGH input row, the ideal topology helper finds a conducting pull-down path, so the output is LOW. Real logic gates depend on voltage thresholds, finite drive, leakage, propagation delay, noise margins, tolerances, finite precision, and measurement uncertainty.
A truth-table row is a checked circuit case before it is a table cell. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
One row starts as physical inputs
This row uses two HIGH inputs, each represented by the high rail voltage.
HIGH, HIGH inputs
The row output follows the network
The helper finds a conducting pull-down path, so the output row is LOW. The row is not accepted because someone typed a label.