Question

what is an upside down U in intergers

Answer 1

It's probably referring to an "intersection"

Answer 2

if
S={1,2,3,4,5,6} and G = {2,4,6,8,9,11}
\[S \cap D = {{2,4,6}}\]

Answer 3

if you want the curly braces in math mode use \{ and \}

\[S \cap D = \{2,4,6\}\]

Answer 4

ahh ty