The pic code below intends to specify a tailless arrow. (Linewid, not so intuitively, sets the default length of horizontal line segments.) .PS linewid = 0 arrow right .PE Pic balks: "cannot draw arrow on object with zero length". Yet a point and a direction are all one needs to place an arrowhead. (The current point in the example is (0,0).) A workaround is to make linewid smaller than arrowht (the length of an arrowhead) but not zero. Nevertheless, the example violates Kernighan's law about handling zeros, "Do nothing gracefully."
