>There were no Greek letters on the keypunches of that era, so McCarthy used (lambda (x) (+ x x)), and it has survived to this day.
I have a memory of a paper by McCarthy himself where he tells that the first implemented Lisp had a notation close to FORTRAN. S-expressions were only intended for the theory.
This does not seem correct. There was a vision of using M-expressions, (Metalanguage) but it never happened.
>In computer programming, M-expressions (or meta-expressions) were an early proposed syntax for the Lisp programming language, inspired by contemporary languages such as Fortran and ALGOL. The notation was never implemented into the language and, as such, it was never finalized
https://en.wikipedia.org/wiki/M-expression
I have a memory of a paper by McCarthy himself where he tells that the first implemented Lisp had a notation close to FORTRAN. S-expressions were only intended for the theory.