the start of a new adventure

usage.md

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+# Usage
+
+Three steps : initialize, use and terminating.
+
+## Initialize
+
+Call the subroutine `genp_init` with two parameters.
+The first is an integer and must be 0. 
+The second is the filename for recording the plottings instructions,
+if this filename is an empty string, *stdout* will be used.
+
+## Use it
+
+- call genp_move(x, y)
+- call genp_draw(x, y, c)
+
+## Terminator
+
+- call genp_end(0)
+
+
+