Seven bridges spanned the river Pregel,

Many more than might have been expected;

K\"{o}nigsberg's wise leaders were delighted

To have built such very splendid structures

Crowds each ev’ning surged towards the river,

People walked bemused across the bridges,

Pondering a simple-sounding challenge

Which defeated them and left them puzzled.

Here's the problem; see if you can solve it!,

Try it out at home an scraps of paper!,

Starting out and ending at the same spot,

You must cross each bridge just once each ev’ning.

Eulerian graphs all have this restriction:

The degree of any point is even.

That's the oldest graph result

That mankind has ever known.