$$
hif\_production = k\_HIF\_production\_basal + k\_HIF\_production\_max * hif\_in^2 / (k\_HIF\_pos\_feedback + hif\_in^2)
$$
$$
hif\_degradation = k\_HIF\_deg\_basal * hif\_in * oxygen\_ex + k\_HIF\_deg\_lactate * hif\_in * lactate\_in
$$
Finally
$$
\begin{split}
\frac{d (hif\_in) }{d t} = k\_HIF\_production\_basal + k\_HIF\_production\_max * hif\_in^2 / (k\_HIF\_pos\_feedback + hif\_in^2) - \\
k\_HIF\_deg\_basal * hif\_in * oxygen\_ex + k\_HIF\_deg\_lactate * hif\_in * lactate\_in
\end{split}
$$
$$
lactate\_production = k\_lactate\_production * hif\_in^2 / (k\_lactate\_production\_reg + hif\_in^2)
$$
$$
lactate\_degradation = k\_lactate\_deg\_basal * lactate\_in
$$
$$
lactate_transport = (k\_MCT1 * lactate\_ex - k\_MCT4 * lactate\_in)
$$
Finally
$$
\begin{split}
\frac{d (lactate) }{d t} =k\_lactate\_production * hif\_in^2 / (k\_lactate\_production\_reg + hif\_in^2) - \\
k\_lactate\_deg\_basal * lactate\_in + \\
(k\_MCT1 * lactate\_ex - k\_MCT4 * lactate\_in)
\end{split}
$$
$$
\begin{split}
\frac{d (GFP) }{d t} =k\_GFP\_production\_constantFP\_production * hif\_in^3 / (k\_GFP\_production\_constant + hif\_in^3) - \\
k\_GFP\_deg * gfp\_in
\end{split}
$$
$$
\frac{d (Oxygen\_ext) }{d t} = - k\_min\_o2\_deg - k\_max\_o2\_deg / ((hif\_in / HIF\_threshold)^{hill\_coeff\_o2\_deg} + 1)
$$