public static PatternExpression getDefiningExpression(OperandSymbol sym) {
		PatternExpression patexp = sym.getDefiningExpression();
		if (patexp != null) {
			return patexp;
		}
		TripleSymbol defSym = sym.getDefiningSymbol();
		if (defSym == null) {
			return null;
		}
		patexp = defSym.getPatternExpression();
		return patexp;
	}
Obtains the "defining expression"

<p>
This is either the symbol's assigned defining expression, or the expression associated with
its defining symbol.

@return the defining expression, or null if neither is available
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/app/plugin/assembler/sleigh/expr/OperandValueSolver.java