--o
| dA_i    | {(da_i), da_i}    | Differential      |  D                |
|         |                   | dimension i       |                   |
o---------o-------------------o-------------------o-------------------o
| dA      | &lt;|d!A!|&gt;          | Tangent space     |  D^n              |
|         | &lt;|da_i,...,da_n|&gt; | at a point:       |                   |
|         | {&lt;da_i,...,da_n&gt;} | Set of changes,   |                   |
|         | dA_1 x ... x dA_n | motions, steps,   |       