all four now use lexical scope. Scheme also supports dynamic scope. 1-lisp or 2-lisp is also a difference, though all support lexical closures and function obj

all four now use lexical scope. Scheme also supports dynamic scope. 1-lisp or 2-lisp is also a difference, though all support lexical closures and function objects. Racket now has a variant without s-expressions. That's also a huge difference.