in reply to How do I efficiently predeclare a hash with a set of keys

The most efficient way to initialize a hash (other than directly, i.e. %h = ( key => value, ...)) is to assign hash slices: 

@set{5,6,8..53,62..106} = ();

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(Note that this makes the values all undef.)

This technique works particularly well when using hashes as sets, as you are.

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