Choosing between several rules for a single targed based on prerequisites avaibility

[Yannick Patois]

Hi,

I have a target (A) that can be build either by applying a given rule on
a prerequisites (P1) or another rule on another prerequisites (P2).

I would like a Makefile that does:
- If only one of P1 or P2 exists, use the available rule to build it
- If both exists, use P1

Is there a way to say that in a Makefile?
I couldnt find anything about this.

Thanks,

        Yannick

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