BUILT-IN MATHEMATICA SYMBOL

MemberQ

MemberQ[list, form]
returns True if an element of list matches form, and False otherwise.

MemberQ[list, form, levelspec]
tests all parts of list specified by levelspec.

Details and Options Details and Options

form can be a pattern.
The first argument of MemberQ can have any head, not necessarily List.
MemberQ[list, form] immediately tests whether any expression in list matches form; Element[x, dom] asserts that x is an element of the symbolic domain dom.
MemberQ uses standard level specifications:
n levels through n

Infinity levels through Infinity

{n} level n only

{n₁,n₂} levels through
The default value for levelspec in MemberQ is .
A positive level n consists of all parts of expr specified by n indices.
A negative level -n consists of all parts of expr with depth n.
Level consists of numbers, symbols, and other objects that do not have subparts.
Level corresponds to the whole expression.
With the option setting Heads->True, MemberQ looks at heads of expressions and their parts.