Nested functions

I was checking out your function and thinking of trying to make it more 
efficient when I noticed your comment above. 

:-D

Yes, bioinformatics is full 
of this stuff - have a look at Bioconductor.

I'm about it, but it'll take some time. It's a vast repository...

For the meantime, I've attached a graph for clarification ;-)
Dashed lines are followed if the test returns FALSE, solid if TRUE.

Cheers,
John
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