few fixes

Author: thelfer

docs/web/bindings-python-finite_strain.md

@@ -34,7 +34,7 @@ now formulated with Hencky strain measures
 instead of the linearized strain
 ($\boldsymbol{\varepsilon}=\boldsymbol{\varepsilon}^\text{e}+\boldsymbol{\varepsilon}^\text{p}$).
 The small-strain elastoplastic component is the same as in the companion
-[small-strain demo](mgis_small_strain.ipynb).
+[small-strain demo](bindings-python-small_strain.html).
 
 The following implementation shows:
 
@@ -208,11 +208,11 @@ for specific variants of the tangent operators such as:
 - `DCAUCHY_DF`/`DSIG_DF`: \(\dfrac{\partial\boldsymbol{\sigma}}{\partial \boldsymbol{F}}\),
 - `DPK1_DF`: \(\dfrac{\partial\boldsymbol{P}}{\partial \boldsymbol{F}}\),
 - `DS_DEGL`: \(\dfrac{\partial\boldsymbol{S}}{\partial \boldsymbol{E}^\text{GL}}\),
-- `DTAU_DDF`: \(\dfrac{\partial\boldsymbol{\tau}}{\partial \boldsymbol{D}}\).
+- `DTAU_DDF`: \(\dfrac{\partial\boldsymbol{\tau}}{\partial \Delta\,\boldsymbol{F}}\).
 
 where $\boldsymbol{E}^\text{GL}$ is the Green-Lagrange strain,
-$\boldsymbol{\tau}$ the Kirchhoff stress and \(\boldsymbol{D}\) the
-deformation rate gradient.
+$\boldsymbol{\tau}$ the Kirchhoff stress and \(\Delta\,\boldsymbol{F}\) is given by
+\(\left.\boldsymbol{F}\right|_{t+dt}\,\cdot\,\left.\boldsymbol{F}\right|_{t}^{-1}\).
 
 
 ```python

docs/web/ipynb/mgis_finite_strain.ipynb

@@ -112,7 +112,7 @@
     "\\texttt{DTAU\\_DDF}:\\qquad & \\dfrac{\\partial\\boldsymbol{\\tau}}{\\partial \\boldsymbol{D}}\\\\\n",
     "\\end{align*}\n",
     "$$\n",
-    "where $\\boldsymbol{E}^\\text{GL}$ is the Green-Lagrange strain, $\\boldsymbol{\\tau}$ the Kirchhoff stress and $ \\boldsymbol{D}$ the deformation rate gradient."
+    "where $\\boldsymbol{E}^\\text{GL}$ is the Green-Lagrange strain, $\\boldsymbol{\\tau}$ the Kirchhoff stress and $\\Delta\\,\\boldsymbol{F}$$ is given by $\\left.\\boldsymbol{F}\\right|_{t+dt}\\,\\cdot\\,\\left.\\boldsymbol{F}\\right|_{t}^{-1}$$.\n"
    ]
   },
   {