Data structures for quasistrict higher categories

We present new data structures for quasistrict higher categories, in which associativity and unit laws hold strictly. Our approach has low axiomatic complexity compared to traditional algebraic approaches, and gives a practical method for performing calculations in quasistrict 4-categories. It is amenable to computer implementation, and we exploit this to give a machine-verified algebraic proof that every adjunction of 1-cells in a quasistrict 4-category can be promoted to a coherent adjunction satisfying the butterfly equations.