all of these should give errors:

    o34 = new HashTable from {asdf => foo}

    i35 : inverse matrix {{1,2}}

    o35 = | 1 |
	  | 0 |

		   2        1
    o35 : Matrix ZZ  <--- ZZ

    i36 : ( matrix {{1,2}} )^-1

    o36 = | 1 |
	  | 0 |

		   2        1
    o36 : Matrix ZZ  <--- ZZ

    i39 : ( matrix {{1},{2}} )^-1
    stdio:39:21:(3):[0]: error: matrix not invertible

    i40 : inverse matrix {{1},{2}}
    stdio:40:1:(3):[0]: error: matrix not invertible
