c.trace();
System.err.println("   " + c.trace());
static void traceback(iClosure c, int n) {    if (c == null) {			// if end of the line    	return;    }    if (n == 0) {			// if recursion limit reached    	System.err.println("   ...");	return;    }    traceback(c.parent, n - 1);		// print ancestry first    c.trace();				// report this closure}