Global macro: How to remove a variable?

I created a macro of available variable names in my dataset ($vitamins):

Code:

global vitamins vita vitb vitc vitd vite

I created another macro of variables names which I would like to exclude ($vitamins_to_exclude):

Code:

global vitamins_to_exclude vitd vite

I would like to generate a third macro of variable names which I would like to include in my analyses ($vitamins_to_include), but both of these command don't work:

Code:

global vitamins_to_include $vitamins - $vitamins_to_exclude

Code:

global vitamins_to_include : list $vitamins - $vitamins_to_exclude

What is wrong with these commands? How can I code this correctly?

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