Show that |= ∃x (Dx → ∀x Dx).

Answer 1

   1.Da            Assume for Conditional Proof/Introduction

   2.∀x Dx          1, Universal Generalization/Introduction

3.Da -> ∀x Dx       1-2, Conditional Proof/Introduction

4.∃x(Dx -> ∀x Dx)    3, Existential Generalization/Introduction

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