Unspecified mappings.

Either (although not both) of a transformation's mappings may be left unspecified by omitting the right hand sides (and `$=$' signs) from all the relevant transformation functions. Thus, the transformation given by:

Forward $\left\{ \mbox{ \begin{tabular}{l} \lq \texttt{p = ALPHA + 2}' \\ \lq \texttt{q = 44 - 2 * OMEGA}' \\ \end{tabular}}\right.$

Inverse $\left\{ \mbox{ \begin{tabular}{l} \lq \texttt{ALPHA}' \\ \lq \texttt{OMEGA}' \end{tabular}}\right.$

has only the forward mapping defined (the remainder of the inverse functions serves simply to define the names of the input variables). To define only the inverse mapping, the right hand sides of all the forward transformation functions would be omitted instead.