Hey! OP here
Great question - h' in Equation 1a refers to the derivative of h with respect to time (t). This is a differential equation which we can solve mathematically when we have x in order to get a closed-form solution for h.
We would then plug in that h (the hidden state) into equation 1b.
In our case, we don't actually wait for a closed-form solution but instead compute the discrete representation (Equation 2)
In our case, we don't actually wait for a closed-form solution but instead compute the discrete representation (Equation 2)
Hope that helps!