If f is a dyad, then

f/ 2 4 5


2 f 4 f 5

where the rightmost occurence of f is invoked first. I am wondering if
there is a smart way to recognize this first invocation separately from the
rest. This will enable me to perform some initialization inside f. By
"smart" I mean something smarter than the followung two:

1) using side effect like setting a global flag.
2) adding some signature structure to the output of f (eg, 'inited';
    and then checking the absence of this signature.

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