(* simple variables *) f := {x => x}; f := {_ => x}; (* literals *) f := {"foo" => "!"}; f := {Bar => "?"}; f := {55 => "~"}; (* tuples *) f := {<> => x}; f := {<x> => x}; f := {<x,y> => x}; f := {<x,y,z> => x};