`heap`recordThe heap data-structure

`>?`- Greater-than relation for keys
`<?`- Less-than relation for keys
`inf`- Infinity w.r.t. the inequality `>?'
`data`- Vector data-store underlying heap
`size`- Size of the heap as distinct from size of data
`membership`- Mapping from data to indices

(define-record-and-printer heap >? <? inf data size membership)