func SetMapReduce[Elt comparable, Result, Accumulator any](mapFn func(Elt) Result, reduceFn func(Accumulator, Result) Accumulator) func(map[Elt]sets.Empty) Accumulator {
	return func(set map[Elt]sets.Empty) Accumulator {
		var ans Accumulator
		for elt := range set {
			ans = reduceFn(ans, mapFn(elt))
		}
		return ans
	}
}

// SliceMapReduce is map-reduce starting from a slice.

	var mapFn ir.Node
	switch {
	case n.Assigned:
		mapFn = mapfn(mapassign[fast], t, false)
	case t.Elem().Size() > abi.ZeroValSize:
		args = append(args, reflectdata.ZeroAddr(t.Elem().Size()))
		mapFn = mapfn("mapaccess1_fat", t, true)
	default:
		mapFn = mapfn(mapaccess1[fast], t, false)
	}
	call := mkcall1(mapFn, nil, init, args...)
	call.SetType(types.NewPtr(t.Elem()))

	case 2:
		return typecheck.LookupRuntime(name, t.Elem(), t.Elem())
	}
	base.Fatalf("chanfn %d", n)
	return nil
}

func mapfn(name string, t *types.Type, isfat bool) ir.Node {
	if !t.IsMap() {
		base.Fatalf("mapfn %v", t)
	}
	if mapfast(t) == mapslow || isfat {
		return typecheck.LookupRuntime(name, t.Key(), t.Elem(), t.Key(), t.Elem())
	}

	//   a = *var
	a := n.Lhs[0]

	var call *ir.CallExpr
	if w := t.Elem().Size(); w <= abi.ZeroValSize {
		fn := mapfn(mapaccess2[fast], t, false)
		call = mkcall1(fn, fn.Type().ResultsTuple(), init, reflectdata.IndexMapRType(base.Pos, r), r.X, key)
	} else {
		fn := mapfn("mapaccess2_fat", t, true)
		z := reflectdata.ZeroAddr(w)

                public int size() {
                    return 1;
                }
            };
        }
    }

    private static class MapN<K, V> extends AbstractImmutableMap<K, V> {
        private final Object[] entries;

        private MapN(Map<K, V> map) {
            if (map != null) {
                entries = new Object[map.size()];
                int idx = 0;

                public int size() {
                    return 1;
                }
            };
        }
    }

    private static class MapN<K, V> extends AbstractImmutableMap<K, V> {
        private final Object[] entries;

        private MapN(Map<K, V> map) {
            if (map != null) {
                entries = new Object[map.size()];
                int idx = 0;

function findClosestElementInSortedArray(ary,mapFn,val,maxDiff){if(ary.length===0)return null;let aftIdx=findLowIndexInSortedArray(ary,mapFn,val);const befIdx=aftIdx>0?aftIdx-1:0;if(aftIdx===ary.length)aftIdx-=1;const befDiff=Math.abs(val-mapFn(ary[befIdx]));const aftDiff=Math.abs(val-mapFn(ary[aftIdx]));if(befDiff>maxDiff&&aftDiff>maxDiff)return null;const idx=befDiff<aftDiff?befIdx:aftIdx;return ary[idx];}

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