Before revision: An ideal current source has zero conductance (infinite resistance) and so adds nothing to the denominator.Wadhwa, p. 88 Ideal voltage sources When computing the equivalent conductance all the generators have to be switched off, so all voltage generators become short circuits.
After revision: An ideal current source has zero conductance (infinite resistance) and so adds nothing to the denominator.Wadhwa, p. 88 Ideal voltage sources