typo usigned->using

Author: plops

06-anti-grain.rst

@@ -290,7 +290,7 @@ border (with some tolerance or we won't see anything).
 Geometrical primitives
 ++++++++++++++++++++++
 
-We need now to define a few primitives usigned signed distance function. You'll
+We need now to define a few primitives using signed distance function. You'll
 understand in the next section why we only need a few primitives. In the
 meantime, we'll use a less boring palette than the one in the previous
 section. We'll use instead the palette that has become the standard for