Join Semilattice
#束論
#Lattice_Theory
https://en.wikipedia.org/wiki/Semilattice
https://ja.wikipedia.org/wiki/結びと交わり
Idempotent Law (冪等性):
$ a \vee a = a
Associative Law (結合性):
$ a \vee (b \vee c) = (a \vee b) \vee c
Commutative Law (可換性):
$ a \vee b = b \vee a