[exim] Different ACL Condition Combinations

[MRob via Exim-users]

I think one combine boolean conditions sevral ways. Are these all same? 
Is there performance reasons or functional reason to choose which one--- 
or is it no different, only choose for readability?

warn condition = ${if <condition 1>}
     condition = ${if <condition 2>}
     <do something>
warn condition = ${if and {{<condition 1>}{<condition 2>}}}
     <do something>

warn condition = ${if <condition 1>{${if <condition 2>}}fail}
     <do someting>

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