Erlang映射is_key

-module(helloworld). 
-export([start/0]). 

start() -> 
   Lst1 = [{"a",1},{"b",2},{"c",3}], 
   Map1 = maps:from_list(Lst1), 
   io:fwrite("~p~n",[maps:is_key("a",Map1)]).