Plotting CAS expressions with the Function App [SOLVED]

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Using the ilapalce command in CAS, I have obtained an expression in the variable t.

Now I want to plot this function using the Function App, so I run the App and import the CAS expression pressing the Menu key and selecting Get from CAS. Then, before pressing Ok I have to manually substitute X for t all over the expression, because X is the only variable name accepted by the Function App.

What I'd like to knows is if there is an easer way to substitute X for t in CAS before switching to the Function App, or inside the Function App.

The command subst(expression, t=X) does not work because X is a real variable with default value 0.