How to write a function to test if a cell contains a specific variable?

The cell can contains any characters, for example, how to write a function to test if there is a specific variable in the cell?

Given:
1) Variable can be only letter.
2) The cell string is in UPPER case status, so no need to consider LOWER case letter.

Examples, test if below equation contains variable ABC:
(ABCD + BHY)*2 > BUJ : It should return FALSE, since ABCD is not same as ABC.
(AABC + BHY)*2 > BUJ : It should return FALSE, since AABC is not same as ABC.
(KABCD + BHY)*2 > BUJ : It should return FALSE, since KABCD is not same as ABC.
(ABCD + BHY)*2 > ABC : It should return TRUE.
ABC + BHY*2 > BUJ : It should return TRUE.

Thanks.

Formula:

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Function CheckStr(StrLookIn As String, StrLookFor As String) As Boolean

I would like to have a function like this, in this case StrLookIn is the equation string, StrLookFor is ABC

Thanks.

Formula:

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You are using a strange character instead of a space.

I over typed your spaces with a space and it worked.

It is just not that simple, I think it requires a few steps:

1) Use Instr and check if it contains ABC. If yes and if there is a character before or after the ABC, we need to check the character, if the character is one of capital letter, then this is not the variable I am looking for. If no capital letter before/after that ABC or the character is not capital letter, then return TRUE, then end. If it is FALSE for first ABC, then move to below step.
2) If above string is not the variable I am looking for, I need to identify that variable containing ABC, and replace that variable with blank, for example, I need to change (AABC + BGH)*2 > KKP to ( + BGH)*2 > KKP, and I still need to use Instr to check if ( + BGH)*2 > KKP contains variable ABC, and so on, until Instr returns 0. But as long as I found variable ABC, I can return TRUE and exit the loop without reaching Instr=0.