Collocation tableau row-sum identity ($A1=c$)

For a collocation Runge-Kutta method, $a_{ij}={\int }_0^{c_i}{\ell }_j(t)dt$, where the Lagrange interpolation basis obeys ${\sum }_j{\ell }_j=1$. Hence each row sum is its collocation node. Failure of this identity disproves a claimed collocation tableau with those nodes. The identity alone is necessary rather than sufficient: the individual integrated basis coefficients must also agree.