>that indentation only would be sufficient to write many Lisp structures? Lisp's syntax is just a textual representation of the internal abstract syntax tree,

>that indentation only would be sufficient to write many Lisp structures? Lisp's syntax is just a textual representation of the internal abstract syntax tree, so you could represent it any number of ways: s-expressions, indentations, even something like json. I think s-expressions were just the absolute simplest way to represent them with the smallest parser required. It's really really not much.