--- ray/src/px/greyscale.c	1993/06/04 14:46:44	2.3
+++ ray/src/px/greyscale.c	1995/02/14 08:55:09	2.4
@@ -62,7 +62,7 @@ char  *argv[];
 greyscale(col0)			/* output our grey scale */
 COLOR  col0;
 {
-	double  exp();
+	extern double  exp();
 	COLOR  col1, col2, scanline[512];
 	double  x;
 	int  j;