grdcontour(1gmt) on Linux
The text 4c6958168ea7, as Debian 8 (Jessie), Debian 7 (Wheezy), Debian 6.0 (Squeeze), Debian 5.0 (Lenny), Debian 4.0 (Etch), Debian 3.1 (Sarge) shipped it.
contouring of 2-D gridded data sets
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