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prove the following sequent:

1. $(\exists x) Fx \to (\forall x) Gx \vdash (\exists x)(Fx \to (\forall x)Gx)$

2. $(\forall x)(Fx \to (\forall y)\neg Fy) \vdash \neg(\exists x)Fx$

3. $(\exists x)Fx, (\forall x)(Fx \; à \; Gx) \vdash (\exists x)G$