## A More Complex Example

If given the premise that

$$1+2^{2}=5$$

one can prove that

$$1\in \epsilon[\lambda z \, z+2^{2} =5]$$

For it follows from our premise (by $$\lambda$$-Abstraction) that:

$$[\lambda z \, z+2^{2}=5]1$$

Independently, by the logic of identity, we know:

$$\epsilon[\lambda z \, z+2^{2}=5] = \epsilon[\lambda z \, z+2^{2}=5]$$

So we may conjoin this fact and the result of $$\lambda$$-Abstraction to produce:

$$\epsilon[\lambda z \, z+2^{2}=5] \eqclose \epsilon[\lambda z \, z+2^{2}=5] \amp [\lambda z \, z+2^{2}=5]1$$

Then, by existential generalization on the concept $$[\lambda z \, z+2^{2}=5]$$, it follows that:

$$\exists G[\epsilon[\lambda z \, z+2^{2}=5] \eqclose \epsilon G \amp G1]$$

And, finally, by the definition of membership, we obtain:

$$1\in\epsilon[\lambda z \, z+2^{2}=5]$$,

which is what we were trying to prove.

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