How to program y is reachable from x?

rbigui

This ordering is for detecting prime invisible tasks [paper: Mining Process Models with Prime Invisible Tasks]

Case 1: If y is equal to x, t is of type short skip

Case 2: If y is reachable  from x, t is of type long skip
Case 3: If a is equal to b, t is of short redo type

Case 4: If a is reachable from b, t is of long redo type

The code for Case 1 is as follows:

public static strictfp <E> double[][] constructBooleanShortSKIPIvTAbstractionMatrix(CausalAbstraction<E> ca,
			DirectlyFollowsAbstraction<E> dfa, ParallelAbstraction<E> pa) {
		double[][] shortskip = new double[ca.getMatrix().length][ca.getMatrix().length];
		for (int a = 0; a < ca.getEventClasses().length; a++) {
			for (int b = 0; b < ca.getEventClasses().length; b++) {
				if (ca.holds(a, b)) {
				  for (int x : ca.getAllIndicesGeqForRow(a)) {
				  for (int y : ca.getAllIndicesGeqForColumn(b)) {
					 if (x == y && !dfa.holds(y, x) && !pa.holds(x, b) && !pa.holds(a, y)) {
								shortskip[a][b] = DEFAULT_THRESHOLD_BOOLEAN;
							} } } } } }
		return shortskip;

Can anyone help me to code Case 2? I don't know how to program y is reachable from x.

Please, I extremely need your help. I'm not a programmer but I have to programme a part of a paper that I am working on and the definition above is included in the framework. 

Thank you