Diagram chasing is a method of mathematical proof used especially in homological algebra. Given a commutative diagram, a proof by diagram chasing involves the formal use of the properties of the diagram, such as injective or surjective maps, or exact sequences. A syllogism is constructed, for which the graphical display of the diagram is just a visual aid. It follows that one ends up "chasing" elements around the diagram, until the desired element or result is constructed or verified.
Examples of proofs by diagram chasing include those typically given for the five lemma, the snake lemma, the zig-zag lemma, and the nine lemma.
Read more about this topic: Commutative Diagram
Famous quotes containing the words diagram and/or chasing:
““God’s fire upon the wane,
A diagram hung there instead,
More women born than men.””
—William Butler Yeats (1865–1939)
“You know lots of criticism is written by characters who are very academic and think it is a sign you are worthless if you make jokes or kid or even clown. I wouldn’t kid Our Lord if he was on the cross. But I would attempt a joke with him if I ran into him chasing the money changers out of the temple.”
—Ernest Hemingway (1899–1961)