Slight performance improvement and simplification of delete implementation
Slight performance improvement and simplification of delete implementation

tobgu/pyrsistent,Futrell/pyrsistent,tobgu/pyrsistent,tobgu/pyrsistent,jkbjh/pyrsistent,jkbjh/pyrsistent,jml/pyrsistent,Futrell/pyrsistent,jkbjh/pyrsistent,jml/pyrsistent,Futrell/pyrsistent,jml/pyrsistent