TITLE: History of the notation for substitution
QUESTION [20 upvotes]: One of the very common notations for syntactic substitution is $[\ /\ ]$.
However, there seems to be an inconsistency in the literature about its usage. 

Many write $[t/x]$ for "substitute $t$ for $x$" (Girard, Buss, ...). 
Others use $[x/t]$ for "replace $x$ with $t$" (van Dalen, Troelstra, Martin-Löf, ...).

I am wondering about the history of this notation. 
In particular, 
who was the first person to use this notation for 
syntactic substitution in logic?

REPLY [4 votes]: (To the title question, and @AnstenKlev’s answer:) 
Sarrus (1848) introduced maybe the earliest signe de substitution : $\style{font-family:sans-serif;font-style:italic}1\,^t_x$.