Sentence:  If the vertex is at **f , and if the interior of C is on the <WSD>left</WSD> as one moves in the direction of increasing t , then every such corner can be found from the curve obtained by rotating C clockwise through 90 ` about the vertex . 
Meaning of the word marked with <WSD> tags:  being or located on or directed toward the side of the body to the west when facing north