A DEC-2060 system was introduced in the fall of 1982, allowing us to use Edinburgh Prolog .
I wrote an emulator of its subset on Edinburgh Prolog in the summer of 1983, in about one week when the DEC-2060 was lightly loaded because most of the other users were away on summer vacation.
Actual coding and debugging of the system began in the fall of 1983 using the implementation on Edinburgh Prolog, by a team of some 30 programmers gathered from several software companies.
The original PSI machine ran at about the same speed as Edinburgh Prolog on a DEC 2060.
The use of the ampersand for logical conjunction and the semicolon as clause separator is different from Edinburgh Prolog syntax.
Unfortunately, the conjunction symbol & has the same control meaning as in Edinburgh Prolog, namely, for sequential goal satisfaction; but in concurrent logic languages and herein, , is used to denote parallel conjunction.
Again this is contrary to the use of the period in Edinburgh Prolog and due to another historical mistake.
Some superficial differences between Parlog84 and Parlog86 are accounted for by a syntax change closer to Edinburgh Prolog, and the explicit precedence of parallel connectives over sequential ones.