WolframLang: Atomic Expression

An atom is a indivisible Expression .

An atom is one of:

• number
• Symbol
• String
• Special Characters such as \[Pi], \[Alpha].

AtomQ[expr]

return True if expression is a atom, else False. AtomQ

(* all True *)
AtomQ[ 3 ]
AtomQ[ 3.1 ]
AtomQ[ 3/4 ]
AtomQ[ Pi ]
AtomQ[ I ]
AtomQ[ 3 + I ]
AtomQ[ x ]
AtomQ[ "some" ]

AtomQ[ {} ] === False
AtomQ[ f[] ] === False
AtomQ[ x + y ] === False