HP Prime Define: Use with solve, etc.

[Helge Gabert]

Here is a question:

If I define a function in "Function" App, I can use that within solve() in CAS view; no problem.

e.g., solve(F2(x)=0,x) returns the solution

If F2(X)=-COSH(X)+9 returns {-LN(4*sqrt(5)+9 , . . . }

However, if I define a function with "Define", it doesn't work.

e.g., solve(MYFUNC(x or X or 'X' or " 'X' ")=0,x (or variants)) returns {}.

So how do I get a user-defined function (other than built-in F0,...F9) to work inside CAS commands? Thanks!