Theorem suprlubii

Description: The supremum of a nonempty bounded set of reals is the least upper bound. (Contributed by NM, 15-Oct-2004) (Revised by Mario Carneiro, 6-Sep-2014)

	Ref	Expression
Hypothesis	sup3i.1	$$⊢\left(A\subseteq ℝ\wedge A\ne \varnothing \wedge \exists x\in ℝ\forall y\in Ay\le x\right)$$
Assertion	suprlubii	$$⊢B\in ℝ\to \left(B<sup\left(A,ℝ,<\right)\leftrightarrow \exists z\in AB<z\right)$$

Proof

Step	Hyp	Ref	Expression
1		sup3i.1	$$⊢\left(A\subseteq ℝ\wedge A\ne \varnothing \wedge \exists x\in ℝ\forall y\in Ay\le x\right)$$
2		suprlub	$$⊢\left(\left(A\subseteq ℝ\wedge A\ne \varnothing \wedge \exists x\in ℝ\forall y\in Ay\le x\right)\wedge B\in ℝ\right)\to \left(B<sup\left(A,ℝ,<\right)\leftrightarrow \exists z\in AB<z\right)$$
3	1 2	mpan	$$⊢B\in ℝ\to \left(B<sup\left(A,ℝ,<\right)\leftrightarrow \exists z\in AB<z\right)$$