= Solution
An <ideal operational amplifier> has infinite differential <open-loop gain>, infinite <input impedance>, zero <output impedance>, unlimited <bandwidth> and <slew rate>, and zero <input offset voltage>, <input bias current> and intrinsic <noise>. The idealized model has no finite output-swing or output-current limit.
The usual circuit rules are
$$
\boxed{i_+=i_-=0,\qquad v_+=v_-\ \text{under stable, unsaturated negative feedback}.}
$$
The first follows from infinite <input impedance>. The second follows because a finite output requires $v_+-v_-=v_o/A\to0$ as the <open-loop gain> tends to infinity. It is a virtual equality of potentials, not a conducting connection between the inputs. It cannot be imposed for open-loop operation or after an amplifier reaches its supply rails.
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