unified language for form-compilers

 UFL (Unified Form Language) is a unified language for definition of
 variational forms intended for finite element discretization. More precisely,
 it defines a fixed interface for choosing finite element spaces and defining
 expressions for weak forms in a notation close to mathematical notation.
 The form compilers FFC and SyFi use UFL as their end-user interface,
 producing UFC implementations as their output.