λa + λb + λc + λd + ... = y as [λ, λ, λ, λ, ..., y] ...

Under the conditions of the Hamiltonian principle, information is exchanged between two masses during an interaction by ...

An important part of econometrics is concerned with developing methods for analyzing relationships in multi-equation models, with due regard to (a) the non-experimental, multi-causal nature of most ...