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diff --git a/ch7/7-09_isupper-time-space.c b/ch7/7-09_isupper-time-space.c
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+++ b/ch7/7-09_isupper-time-space.c
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+#include <stdio.h>
+#include <string.h> /* strchr */
+
+/* The C Programming Language: 2nd Edition
+ *
+ * Exercise 7-9: Functions like `isupper` can be implemented to save space
+ * or to save time. Explore both possibilities.
+ *
+ * Notes: I'm not really sure what they're expecting here. Assuming standard
+ * ASCII, the only uppercase characters are A-Z, and they're all sequential.
+ * Both ways to check seem very lean on necessary resources; I'm unaware of
+ * other methods.
+ */
+
+int isupper_small(int c) {
+	return (c >= 'A' && c <= 'Z');
+}
+
+int isupper_fast(int c) {
+	return (strchr("ABCDEFGHIJKLMNOPQRSTUVWXYZ", c) != NULL);
+}
+
+int main(int argc, char **argv) {
+	int c = 'S';
+	/* The inline conditional makes things more "human-friendly". */
+	printf("is '%c' uppercase? %c\n", c, isupper_fast(c) ? 'y' : 'n');
+	c = 'f';
+	printf("...what about '%c'? %c\n", c, isupper_small(c) ? 'y' : 'n');
+	c = ':';
+	printf("Does a colon have an uppercase variant? %c\n", isupper_small(c) ? 'y' : 'n');
+	return 0;
+}