Scheme as defined in R5RS is not case sensitive when reading symbols. Guile, on the contrary is case sensitive by default, so the identifiers
are the same in R5RS Scheme, but are different in Guile.
It is possible to turn off case sensitivity in Guile by setting the
case-insensitive. More on reader options can be
found at (see Reader options).
Note that this is seldom a problem, because Scheme programmers tend not to use uppercase letters in their identifiers anyway.