The earliest concrete evidence for pre-scheme I can find is that version 0.52 of Scheme 48 (1998) has a prescheme directory [1]. It lists a handful of releases

The earliest concrete evidence for pre-scheme I can find is that version 0.52 of Scheme 48 (1998) has a prescheme directory [1]. It lists a handful of releases going back as far as 1986, though who knows at what point pre scheme was introduced. [1] https://www.s48.org/previous-releases.html https://www.s48.org/previous-releases.html