how to restore latex_name

edit

I wonder how to restore the latex_name attribute of a function or variable after saving to a file

my code is:

fx = function('fxf', latex_name=r'f_x')(y);
eq = fx.diff(y)

then I save the equation with

save(eq,'eq')

In a new session I do

fx = function('fxf', latex_name=r'f_x')(y)
eq=load('eq')

but

show(latex(eq))

does not show the latex expression for f_x but sill stays with diff(fxf(y),y) How can I restore the latex output with "f_x"?