Γ‐Fe2O3@Cu3Al‐LDH‐TUD as a new Amphoteric, Highly Efficient and Recyclable Heterogeneous Catalyst for the Solvent‐free Synthesis of Dihydropyrano[3, 2‐c]pyrazoles and dihydropyrano[3, 2‐c]chromens. (22nd February 2018)