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This paper studies the capacity region of a two-user ergodic interference channel with fading, where only one user is subject to interference from the other user, and the channel state information (CSI) is only available at the receivers. A layered erasure model with arbitrary fading statistics is studied first, whose capacity region is completely determined as a polygon. Each dominant rate pair can be regarded as the outcome of a tradeoff between the rate of the interference-free user and the rate loss its interference causes the other user. Using insights from the layered erasure model, inner and outer bounds of the capacity region are provided for fading Gaussian Z-interference channels. The gap between the inner and outer bounds is no more than 12.8 bits per channel use per user, regardless of the signal-to-noise ratio (SNR) and fading statistics.