``desing/singrc``

Computing the partial derivatives of an element of the coordinate ring
of a chart in a recursive fashion skipping zero derivatives.

**Input:**-
**F**- a pair
*(f,b)* where *f* is an element of the coordinate
ring of some underlying chart and *b* is a nonnegative integer,
**t**- differentiating parameter indicator (in the subtree of
recursive calls only partial derivatives with respect to
parameters with index greater than or equal to
*t* are used), in
the initial call it should be 1.

**Output:**- -

The procedure uses the global variables: **desingSingS**,
**desingSingIND**, **desingSingPDER**, which store the data
of the chart for *F*. The partial derivatives of *f* up to order *b-1*
will be generated in the global variable **desingSingSL**.