case ir.OLITERAL, ir.ONIL, ir.ONAME, ir.OLINKSYMOFFSET, ir.OMETHEXPR,
			ir.OAND, ir.OANDNOT, ir.OLSH, ir.OOR, ir.ORSH, ir.OXOR, ir.OCOMPLEX, ir.OMAKEFACE,
			ir.OADDR, ir.OBITNOT, ir.ONOT, ir.OPLUS,
			ir.OCAP, ir.OIMAG, ir.OLEN, ir.OREAL,
			ir.OCONVNOP, ir.ODOT,
			ir.OCFUNC, ir.OIDATA, ir.OITAB, ir.OSPTR,
			ir.OBYTES2STRTMP, ir.OGETG, ir.OGETCALLERPC, ir.OGETCALLERSP, ir.OSLICEHEADER, ir.OSTRINGHEADER:

		ir.OCONVNOP,
		ir.ODIV,
		ir.ODOT,
		ir.ODOTTYPE,
		ir.OLITERAL,
		ir.OLSH,
		ir.OMOD,
		ir.OMUL,
		ir.ONEG,
		ir.ONIL,
		ir.OOR,
		ir.OOROR,
		ir.OPAREN,
		ir.OPLUS,
		ir.ORSH,
		ir.OSUB,
		ir.OXOR:
		return false
	}

	// Be conservative.
	return true
}

// expand append(l1, l2...) to
//
//	init {
//	  s := l1

        entities.put("sub", "\u2282");
        entities.put("sup", "\u2283");
        entities.put("nsub", "\u2284");
        entities.put("sube", "\u2286");
        entities.put("supe", "\u2287");
        entities.put("oplus", "\u2295");
        entities.put("otimes", "\u2297");
        entities.put("perp", "\u22a5");
        entities.put("sdot", "\u22c5");
        entities.put("lceil", "\u2308");
        entities.put("rceil", "\u2309");

		ir.OLE,
		ir.OGT,
		ir.OGE,
		ir.OKEY,
		ir.OSTRUCTKEY,
		ir.OLEN,
		ir.OMUL,
		ir.OLSH,
		ir.ORSH,
		ir.OAND,
		ir.OANDNOT,
		ir.ONEW,
		ir.ONOT,
		ir.OBITNOT,
		ir.OPLUS,
		ir.ONEG,
		ir.OOROR,
		ir.OPAREN,
		ir.ORUNESTR,
		ir.OREAL,
		ir.OIMAG,
		ir.OCOMPLEX:
		return false

	// Only possible side effect is division by zero.
	case ir.ODIV, ir.OMOD:

		n := n.(*ir.SelectorExpr)
		return n.FuncName()

	case ir.OMIN, ir.OMAX:
		n := n.(*ir.CallExpr)
		return walkMinMax(n, init)

	case ir.ONOT, ir.ONEG, ir.OPLUS, ir.OBITNOT, ir.OREAL, ir.OIMAG, ir.OSPTR, ir.OITAB, ir.OIDATA:
		n := n.(*ir.UnaryExpr)
		n.X = walkExpr(n.X, init)
		return n

	case ir.ODOTMETH, ir.ODOTINTER:
		n := n.(*ir.SelectorExpr)

			} else {
				add.List.Append(r)
			}
			add.SetType(t)
			return add
		}
		n.X, n.Y = l, r
		n.SetType(t)
		return n

	case ir.OBITNOT, ir.ONEG, ir.ONOT, ir.OPLUS:
		n := n.(*ir.UnaryExpr)
		return tcUnaryArith(n)

	// exprs
	case ir.OCOMPLIT:
		return tcCompLit(n.(*ir.CompLitExpr))

	case ir.OXDOT, ir.ODOT:
		n := n.(*ir.SelectorExpr)

	"equiv":    "\u2261",
	"le":       "\u2264",
	"ge":       "\u2265",
	"sub":      "\u2282",
	"sup":      "\u2283",
	"nsub":     "\u2284",
	"sube":     "\u2286",
	"supe":     "\u2287",
	"oplus":    "\u2295",
	"otimes":   "\u2297",
	"perp":     "\u22A5",
	"sdot":     "\u22C5",
	"lceil":    "\u2308",
	"rceil":    "\u2309",
	"lfloor":   "\u230A",
	"rfloor":   "\u230B",
	"lang":     "\u2329",

        flatten(s1) == [dir1.path, "1:dir2/dir3", "1:dir5/and/more"]

        def s2 = s1.plus(dir1dir2dir4)
        flatten(s2) == [dir1.path, "1:dir2", "2:dir3", "2:dir4", "1:dir5/and/more"]

        def s3 = s2.plus(dir6)
        flatten(s3) == [parent.path, "1:dir1", "2:dir2", "3:dir3", "3:dir4", "2:dir5/and/more", "1:dir6"]

        def s4 = s3.plus(dir1dir2)
        flatten(s4) == [parent.path, "1:dir1", "2:dir2", "2:dir5/and/more", "1:dir6"]

     */
    @CheckReturnValue
    public abstract FileHierarchySet plus(File path);

    /**
     * Returns a set that contains the union of this set and the given absolute path. The set contains the path itself, plus all its descendants.
     */
    @CheckReturnValue
    public abstract FileHierarchySet plus(String absolutePath);

    /**

            classpath = classpath.plus(moduleRegistry.getModule("gradle-dependency-management").getAllRequiredModulesClasspath());
            classpath = classpath.plus(moduleRegistry.getModule("gradle-plugin-use").getAllRequiredModulesClasspath());
            classpath = classpath.plus(moduleRegistry.getModule("gradle-workers").getAllRequiredModulesClasspath());