const fs=require('fs'), assert=require('assert/strict');
let cases=0, anchors=0, divergent=0;
for(let n=1;n<=10;n++) {
  const column=Array.from({length:n},(_,i)=>i);
  for(let mask=1;mask<(1<<n);mask++) {
    const selected=new Set(column.filter(id=>mask&(1<<id)));
    const remainder=column.filter(id=>!selected.has(id));
    const reached=new Set();
    for(const anchor of remainder) for(const after of [false,true]) {
      const rawGap=column.indexOf(anchor)+(after?1:0);
      const gap=column.slice(0,rawGap).filter(id=>!selected.has(id)).length;
      reached.add(gap); anchors++;
      assert.equal(gap,remainder.indexOf(anchor)+(after?1:0));
    }
    if(remainder.length) assert.deepEqual([...reached].sort((a,b)=>a-b),Array.from({length:remainder.length+1},(_,i)=>i));
    else assert.equal(selected.size,n); // Only one mathematical gap, all-selected no-op.
    for(const anchor of selected) for(const after of [false,true]) {
      const rawGap=column.indexOf(anchor)+(after?1:0);
      const gap=column.slice(0,rawGap).filter(id=>!selected.has(id)).length;
      const block=column.filter(id=>selected.has(id));
      const normalized=[...remainder.slice(0,gap),...block,...remainder.slice(gap)];
      if(normalized.some((id,i)=>id!==column[i]))divergent++;
      // Object policy intentionally preserves original order for selected anchors.
      // It need not form a contiguous block when this operation is a no-op.
    }
    cases++;
  }
}
const result={passed:true,method:'All nonempty subsets for column lengths 1..10, all unselected and selected Before/After anchors. Order-label equivariance makes separate ID permutations redundant for this reachability property.',cases,unselectedAnchors:anchors,selectedAnchorRawNormalizationDivergences:divergent,conclusion:'Every remainder gap is reachable via an unselected Before/After anchor. Selected-anchor no-op does not remove any possible changed result. Raw-gap and object-anchor policies remain distinct APIs; neither silently supersedes the other.',counterexample:{column:['a','b','c','d'],selected:['b','d'],drop:'Before d',rawGapResult:['a','c','b','d'],objectAnchorResult:['a','b','c','d'],equivalentUnselectedDrop:'After c'}};
fs.writeFileSync(__dirname+'/anchor-results.json',JSON.stringify(result,null,2)+'\n');
console.log(JSON.stringify(result,null,2));