MATLAB: Time derivative then partial derivative of symbolic function

MATLABpartial derivativeSymbolic Math Toolboxtime derivative

In the following code I would like to take the time derivative and then the partial derivative to x and/or y of a symbolic function.
syms x(t) y(t)
f = 4*x^3 + 3*y^2;
g = diff(f,t);
h = diff(g,x(t));
In line 4 an error tells me "Second argument must be a variable or a nonnegative integer specifying the number of differentiations."
How can I alter my code such that I can take this partial derivative?

Best Answer

Just do: 
h = diff(g,x);
and it works.
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