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diff --git a/sys/imio/imaplv.x b/sys/imio/imaplv.x
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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+include	<imhdr.h>
+include	<imio.h>
+
+# IMAPLV -- Transform the logical vector LV (which references an image section)
+# into a physical vector (which references the physical image).
+
+procedure imaplv (im, lv, pv, ndim)
+
+pointer	im
+long	lv[ndim], pv[IM_MAXDIM]
+int	ndim
+int	loff		# logical offset (subscript)
+int	nldims		# number of logical dimensions
+int	i, j		# i = logical dim index, j = physical dim index
+
+begin
+	i = 1
+	nldims = min (IM_NDIM(im), ndim)
+
+	do j = 1, IM_NPHYSDIM(im) {
+	    if (i <= nldims && IM_VMAP(im,i) == j) {
+		loff = lv[i]
+		i = i + 1
+	    } else
+		loff = 1
+	    pv[j] = IM_VOFF(im,j) + IM_VSTEP(im,j) * loff
+	}
+end