Another angle: sometimes students can access e-books through their university's library subscriptions. So if the user is a student, advising them to check with their institution's library could be useful.
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Let me think about the possible intent here. The user might not be aware that the link they're asking for is illegal. Alternatively, they might not have the financial means to buy the book. In that case, maybe recommend affordable options or look for free resources that cover similar topics. But the user did specifically mention the book by K R Gopalakrishna, so alternatives might not be exactly what they need.
Maybe add a note about respecting intellectual property and encouraging them to support authors by purchasing the book. Also, mention that many authors appreciate when their work is used ethically, which can lead to more resources being created.