In Operators§

See primary documentation in context for infix =:=

multi infix:<=:=>(Mu \aMu \b)

Container identity operator. Returns True if both arguments are bound to the same container. If it returns True, it generally means that modifying one will also modify the other.

my ($a$b= (13);
say $a =:= $b;      # OUTPUT: «False␤» 
$b = 2;
say $a;             # OUTPUT: «1␤» 
$b := $a;
say $a =:= $b;      # OUTPUT: «True␤» 
$a = 5;
say $b;             # OUTPUT: «5␤»

The single argument version, called as a routine, will always return True:

say infix:<=:=>(42);    # OUTPUT: «True␤» 
say infix:<=:=>(False); # OUTPUT: «True␤»