diff --git a/10_Expressions/Andrew_exper.Rmd b/10_Expressions/Andrew_exper.Rmd
index 3e1d743..a9faa12 100644
--- a/10_Expressions/Andrew_exper.Rmd
+++ b/10_Expressions/Andrew_exper.Rmd
@@ -17,6 +17,7 @@ is.constant()
 is.elem <- function(x){
   testers <- c(is.call, is.name, is.pairlist, is.atomic)
   tested <- vapply(testers, function(f) f(x), FUN.VALUE = TRUE)
+  if(is.atomic(x) & length(x) > 1) stop("Atomic vectors cannot have length larger than one in an expression.")
   any(tested)
 }
 
@@ -236,4 +237,4 @@ arguements are matched by position
 
 ### Read the documentation and source code for pryr::partial(). What does it do? How does it work? Read the documentation and source code for pryr::unenclose(). What does it do and how does it work?
 
-### The actual implementation of curve() looks more like
\ No newline at end of file
+### The actual implementation of curve() looks more like