"Mary, Mary, Quite Contrary" is a popular English nursery rhyme. The rhyme has been seen as having religious and historical significance, but its origins and meaning are disputed. It has a Roud Folk Song Index number of 19626. == Lyrics == The most common modern version is: The oldest known version was first published in Tommy Thumb's Pretty Song Book (c. 1744) with the following lyrics: Several printed versions of the eighteenth century have the lyrics: The last line has the most variation including: Cowslips all in arow [sic]. and With lady bells all in a row. == Explanations == Like many...

In the mathematics of infinite graphs, an end of a graph represents, intuitively, a direction in which the graph extends to infinity. Ends may be formalized mathematically as equivalence classes of infinite paths, as havens describing strategies for pursuit-evasion games on the graph, or (in the case of locally finite graphs) as topological ends of topological spaces associated with the graph. Ends of graphs may be used (via Cayley graphs) to define ends of finitely generated groups. Finitely generated infinite groups have one, two, or infinitely many ends, and the Stallings theorem about ends...