Merge pull request #56 from rezarastak/modifying_interface

Distinguish const vs non-const interface

diff --cc 9.2/paper.tex
index 443732c9fc1493bc27e393708d8b19ace86c2f3c,ec9dd0e0bfd2104ace641e4b7ba265be909af704..a4f4fd44aa8c2ac52decccbf78ce2c65dfe5b99e
--- 1/9.2/paper.tex
--- 2/9.2/paper.tex
+++ b/9.2/paper.tex
@@@ -278,12 -278,13 +278,13 @@@ that we briefly outline in the remainde
    \item The new \texttt{DiscreteTime} class provides a more
          consistent, more readable, and less error-prone approach to control
          time-stepping algorithms within time-dependent simulations.
-         The interface of this class is designed to be minimal
+         While providing a rich read-only interface, the non-const interface
+         of this class is designed to be minimal
          to enforce a number of important programming invariants, reducing
          the possibility of mistakes in the user code.
 -        An example is that \texttt{DiscreteTime} ensures that the final time step ends
 +        For instance, \texttt{DiscreteTime} ensures that the final time step ends
          precisely on a predefined end time, automatically
 -        lengthening or shortening to final time step.
 +        lengthening or shortening the final time step.
    \item A key component of \dealii{} are the \texttt{FEValues} and
          \texttt{FEFaceValues} classes that evaluate finite element functions
          at quadrature points located on cells and faces of a cell,