How To Append A String Within A String

NSMutableString *string1;
NSMutableString *string2;
string1 = [NSMutableString stringWithString: @"This is a string"];
string2 = string1;
[string2 appendString: @" and it is mine!"];
NSLog (@"string1 = %@", string1);
NSLog (@"string2 = %@", string2);