Concept clusters
Related ideas that live chapters apart, pulled onto one page — every factoring technique, every way to solve a quadratic, and more.
Which multivariable derivative concept do I need?
Total derivative, Jacobian, directional derivative, Hessian -- four related but distinct objects.
5 concepts →
Which topological property does this argument actually need?
Open, closed, compact, and simply connected are four separate properties -- mixing them up breaks a proof.
7 concepts →
d, boundary, and delta: three different-looking ideas that are all the same move
The exterior derivative, the boundary operator, and the first variation each measure a change at the edge of something.
7 concepts →
Reading off grad, div, curl, and the Laplacian in curvilinear coordinates
Every curvilinear vector-operator formula follows the same "divide or multiply by scale factors" pattern.
6 concepts →
Which potential-theory tool answers this question?
Green's identities, Green's functions, and the Helmholtz decomposition all sound alike but do different jobs.
6 concepts →