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The horizontal axis plots z, and marks l over 2 and l, while vertical axis plots I (z, 3 T over 2), and marks I sub 1-plus which is greater than I. The graph plots a square-waveform between 0 and l over 2, with an amplitude of I sub 1-plus. The waveform steps-down to I sub 1-plus plus I sub 1-minus between l over 2 and l before dropping to zero at l. I sub 1-minus is equal to negative gamma sub L times I sub 1-plus.