Add GEB pq checker.

geb/02-meaning-and-form/pq.c

@@ -0,0 +1,54 @@
+#include <stdio.h>
+
+int
+is_theorem_valid(char *candidate)
+{
+	int	 x = 0;
+	int	 y = 0;
+	int	 z = 0;
+	int	 l = 0;
+	char	*p = candidate;
+
+	while (*p != 0) {
+		if (*p == '-') {
+			switch (l) {
+			case 0:
+				x++;
+				break;
+			case 1:
+				y++;
+				break;
+			case 2:
+				z++;
+				break;
+			default:
+				return 0;
+			}
+		}
+		else if (*p == 'p') {
+			l = 1;
+		}
+		else if (*p == 'q') {
+			l = 2;
+		}
+		p++;
+	}
+
+	if ((x + y) == z) {
+		return 1;
+	}
+	return 0;
+}
+
+int
+main(int argc, char *argv[])
+{
+	for (int i = 1; i < argc; i++) {
+		if (is_theorem_valid(argv[i])) {
+			printf("  VALID: %s\n", argv[i]);
+		}
+		else {
+			printf("INVALID: %s\n", argv[i]);
+		}
+	}
+}