declare module 'matrix-utilities' {

  export interface IRow1 {
    0: number;
  }

  export interface IRow3 {
    0: number;
    1: number;
    2: number;
  }

  export interface ICol3 {
    0: IRow1;
    1: IRow1;
    2: IRow1;
  }

  export interface IMatrix3 {
    0: IRow3;
    1: IRow3;
    2: IRow3;
  }

  export function multiply(a: IMatrix3, b: IMatrix3): IMatrix3;
  export function multiply(a: IMatrix3, b: ICol3): ICol3;

  export function flip(a: IMatrix3): IMatrix3;

}