- diff and contract
- contract' -- contract a matrix by a matrix, the dual notion

- contract(Matrix,Matrix) -- contract a matrix by a matrix
- "contract(Matrix,Number)" -- see contract(Matrix,Matrix) -- contract a matrix by a matrix
- "contract(Matrix,RingElement)" -- see contract(Matrix,Matrix) -- contract a matrix by a matrix
- "contract(Matrix,Vector)" -- see contract(Matrix,Matrix) -- contract a matrix by a matrix
- "contract(Number,Matrix)" -- see contract(Matrix,Matrix) -- contract a matrix by a matrix
- "contract(Number,Number)" -- see contract(Matrix,Matrix) -- contract a matrix by a matrix
- "contract(Number,RingElement)" -- see contract(Matrix,Matrix) -- contract a matrix by a matrix
- "contract(Number,Vector)" -- see contract(Matrix,Matrix) -- contract a matrix by a matrix
- "contract(RingElement,Matrix)" -- see contract(Matrix,Matrix) -- contract a matrix by a matrix
- "contract(RingElement,Number)" -- see contract(Matrix,Matrix) -- contract a matrix by a matrix
- "contract(RingElement,RingElement)" -- see contract(Matrix,Matrix) -- contract a matrix by a matrix
- "contract(RingElement,Vector)" -- see contract(Matrix,Matrix) -- contract a matrix by a matrix
- "contract(Vector,Matrix)" -- see contract(Matrix,Matrix) -- contract a matrix by a matrix
- "contract(Vector,Number)" -- see contract(Matrix,Matrix) -- contract a matrix by a matrix
- "contract(Vector,RingElement)" -- see contract(Matrix,Matrix) -- contract a matrix by a matrix
- "contract(Vector,Vector)" -- see contract(Matrix,Matrix) -- contract a matrix by a matrix

The object contract is a method function.