 a word of shape u –, tends to be avoided in positions 9 and 10 in the iambic trimeter), (b) Wilamowitz's Bridge (stating that a spondaic word, of shape – –, is avoided in the same position), (c) Knox's Trochee Bridge (stating that a trochaic word, of shape – u, tends to be avoided in positions 8 and 9), and (d) the law of tetrasyllables (stating that words of the rhythm – – u x are avoided at the end or beginning of a line), have been discovered since Porson's time.These laws apply to different styles or periods of iambic-trimeter writing (neither of the first two bridges mentioned above apply in tragedy, for example).Details of these and other constraints on the trimeter are given in a 1981 article by A.M. Devine and L.D.