From Links to the Mass Matrix

The viewer can (1) write T for an n-link arm in maximal coordinates, (2) say why minimal coordinates are better, (3) derive T = ½q̇ᵀM(q)q̇ with M = Σ Jⁱᵀ𝔗ⁱJⁱ in four moves (sum, substitute, transpose, factor), (4) state and justify: M symmetric, positive definite, depends on q only.