Library
▹
Essentials
▹
Sets
Proposition 1.1.22.
Let
S
be a set. Then:
S
∪ ∅
=
S
Proof.
Trivial.
By
1.1.20
.
References.
https://proofwiki.org/wiki/Union_with_Empty_Set
http://metamath.tirix.org/un0.html
https://leanprover-community.github.io/mathlib_docs/data/set/basic.html#set.union_empty