a) Median spectra of the QSO-lensed images. b) The spectra of images A and B normalized so that their continua have a unit average intensity and are superimposed, and c) the spectral differences between the Hα line profiles in the normalized spectra of images A and B, plotted with error bars for a wavelength bin of 0.004μm. d), e) Same for the pair of images B and C. f), g) Same for the pair of images B and D. Spectra have been filtered with a five-pixel-wide median filter for clarity.