[Maxima] how to call subprogram

[=?Big5?B?tsC4zrav?=]

I defined some function in maxima.
It was called subfun.wxm
such as
C(h,k,r):=(x-h)^2+(y-k)^2=r^2;
......
and so on.

I want to use the functions from subfun.wxm by any maxima program.
How can I to do?
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