This experiment finds out whether `1+x` and `1+` are valid identifiers in the Scheme implementations. They are invalid in all versions of the Scheme standard. We also investigate whether `1+` and `add1` are known procedures.

`1+x` is valid, `1+` is defined, `add1` is defined: Chez, Sizzle

`1+x` is valid, `1+` is not defined, `add1` is defined: Racket, Chicken, SISC

`1+x` is valid, `1+` is defined, `add1` is not defined: MIT, Guile, SCM, XLisp, Rep, Elk, FemtoLisp, Inlab

`1+x` is valid, `1+` is not defined, `add1` is not defined: Gauche, Gambit, Bigloo, Kawa, JScheme, STklos, Shoe, TinyScheme, Scheme 9, BDC, Schemik, Llava, Sagittarius

`1+x` and `1+` are syntax errors, `add1` is defined: Vicare, IronScheme, RScheme, SXM

`1+x` and `1+` are syntax errors, `add1` is not defined: Scheme48/scsh, Larceny, Ypsilon, Mosh, KSi, SigScheme, UMB, Dfsch, Foment, Chibi

`1+x` is read as `1 +x`, `1+` is read as `1 +`, `add1` is not defined: NexJ, Picrin, Owl Lisp